feat(groups): tree repos, hierarchy-aware RBAC, admin API

Server-side foundation for Phase-2 groups (no group-owned resources yet):

Shared types:
- GroupId, Group; App gains group_id; AppRole::{precedence,max} for
  folding the highest effective role across the membership chain.

Repos:
- group_repo: tree CRUD with reparent (ancestor-walk cycle guard under a
  coarse instance-wide structural advisory lock; slug frozen; bumps
  structure_version) and delete=RESTRICT (refuses non-empty groups).
- group_members_repo: per-(user, group) role grants, mirroring app_members.

Hierarchy-aware authz (§5.3):
- AuthzRepo gains effective_app_role / effective_group_role (default to
  direct membership / none, so the ~18 existing test stubs are untouched);
  the Postgres impl resolves each via one depth-bounded recursive CTE that
  MAXes the app's own row with every ancestor group_members row.
- can(): the Member path now folds inherited group roles, so a group_admin
  on any ancestor is implicitly app_admin beneath it. New Capability
  variants InstanceCreateGroup / Group{Read,Write,Admin}; group caps carry
  no app_id (bound API keys can't manage groups). 8 new unit tests.

Admin API:
- groups_api: group CRUD + reparent (admin at both source and destination
  parent, §5.6) + per-group members, all capability-gated.
- apps: POST /apps takes an optional parent group (default root); app
  responses carry group_id; my_role now reflects the effective role.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/manager-core/src/group_members_repo.rs

@@ -0,0 +1,205 @@
+//! CRUD over the `group_members` table — explicit per-(user, group) role
+//! grants. A `group_admin` here is implicitly app_admin on every app and
+//! subgroup beneath the group; that inheritance is resolved by the authz
+//! ancestor walk (`app_members_repo::effective_app_role`), not here.
+//!
+//! Mirrors `app_members_repo` — same three role literals, same shapes.
+
+use async_trait::async_trait;
+use chrono::{DateTime, Utc};
+use picloud_shared::{AdminUserId, AppRole, GroupId, InstanceRole};
+use sqlx::PgPool;
+
+#[derive(Debug, thiserror::Error)]
+pub enum GroupMembersRepositoryError {
+    #[error("database error: {0}")]
+    Db(#[from] sqlx::Error),
+    #[error("invalid app_role stored in DB: {0}")]
+    InvalidRole(String),
+}
+
+#[derive(Debug, Clone)]
+pub struct GroupMembershipRow {
+    pub group_id: GroupId,
+    pub user_id: AdminUserId,
+    pub role: AppRole,
+    pub created_at: DateTime<Utc>,
+}
+
+/// `group_members` row joined with `admin_users` for the dashboard's
+/// per-group Members tab.
+#[derive(Debug, Clone)]
+pub struct GroupMembershipDetail {
+    pub user_id: AdminUserId,
+    pub username: String,
+    pub email: Option<String>,
+    pub instance_role: InstanceRole,
+    pub is_active: bool,
+    pub role: AppRole,
+    pub created_at: DateTime<Utc>,
+}
+
+#[async_trait]
+pub trait GroupMembersRepository: Send + Sync {
+    /// Atomic insert. `None` if a membership already exists (handler → 409).
+    async fn try_insert(
+        &self,
+        group_id: GroupId,
+        user_id: AdminUserId,
+        role: AppRole,
+    ) -> Result<Option<GroupMembershipRow>, GroupMembersRepositoryError>;
+
+    /// Atomic role update. `None` if no row exists (handler → 404).
+    async fn update_role(
+        &self,
+        group_id: GroupId,
+        user_id: AdminUserId,
+        role: AppRole,
+    ) -> Result<Option<GroupMembershipRow>, GroupMembersRepositoryError>;
+
+    /// Remove a membership. No-op when the row doesn't exist.
+    async fn remove(
+        &self,
+        group_id: GroupId,
+        user_id: AdminUserId,
+    ) -> Result<(), GroupMembersRepositoryError>;
+
+    /// Per-group member list joined with `admin_users`, ordered by username.
+    async fn list_for_group_enriched(
+        &self,
+        group_id: GroupId,
+    ) -> Result<Vec<GroupMembershipDetail>, GroupMembersRepositoryError>;
+}
+
+pub struct PostgresGroupMembersRepository {
+    pool: PgPool,
+}
+
+impl PostgresGroupMembersRepository {
+    #[must_use]
+    pub fn new(pool: PgPool) -> Self {
+        Self { pool }
+    }
+}
+
+#[async_trait]
+impl GroupMembersRepository for PostgresGroupMembersRepository {
+    async fn try_insert(
+        &self,
+        group_id: GroupId,
+        user_id: AdminUserId,
+        role: AppRole,
+    ) -> Result<Option<GroupMembershipRow>, GroupMembersRepositoryError> {
+        let row = sqlx::query_as::<_, GroupMembershipRecord>(
+            "INSERT INTO group_members (group_id, user_id, role) \
+             VALUES ($1, $2, $3) \
+             ON CONFLICT (group_id, user_id) DO NOTHING \
+             RETURNING group_id, user_id, role, created_at",
+        )
+        .bind(group_id.into_inner())
+        .bind(user_id.into_inner())
+        .bind(role.as_str())
+        .fetch_optional(&self.pool)
+        .await?;
+        row.map(TryInto::try_into).transpose()
+    }
+
+    async fn update_role(
+        &self,
+        group_id: GroupId,
+        user_id: AdminUserId,
+        role: AppRole,
+    ) -> Result<Option<GroupMembershipRow>, GroupMembersRepositoryError> {
+        let row = sqlx::query_as::<_, GroupMembershipRecord>(
+            "UPDATE group_members SET role = $1 \
+             WHERE group_id = $2 AND user_id = $3 \
+             RETURNING group_id, user_id, role, created_at",
+        )
+        .bind(role.as_str())
+        .bind(group_id.into_inner())
+        .bind(user_id.into_inner())
+        .fetch_optional(&self.pool)
+        .await?;
+        row.map(TryInto::try_into).transpose()
+    }
+
+    async fn remove(
+        &self,
+        group_id: GroupId,
+        user_id: AdminUserId,
+    ) -> Result<(), GroupMembersRepositoryError> {
+        sqlx::query("DELETE FROM group_members WHERE group_id = $1 AND user_id = $2")
+            .bind(group_id.into_inner())
+            .bind(user_id.into_inner())
+            .execute(&self.pool)
+            .await?;
+        Ok(())
+    }
+
+    async fn list_for_group_enriched(
+        &self,
+        group_id: GroupId,
+    ) -> Result<Vec<GroupMembershipDetail>, GroupMembersRepositoryError> {
+        let rows = sqlx::query_as::<_, GroupMembershipDetailRecord>(
+            "SELECT au.id, au.username, au.email, au.instance_role, au.is_active, \
+                    gm.role, gm.created_at \
+             FROM group_members gm \
+             JOIN admin_users au ON au.id = gm.user_id \
+             WHERE gm.group_id = $1 \
+             ORDER BY au.username",
+        )
+        .bind(group_id.into_inner())
+        .fetch_all(&self.pool)
+        .await?;
+        rows.into_iter().map(TryInto::try_into).collect()
+    }
+}
+
+#[derive(sqlx::FromRow)]
+struct GroupMembershipRecord {
+    group_id: uuid::Uuid,
+    user_id: uuid::Uuid,
+    role: String,
+    created_at: DateTime<Utc>,
+}
+
+impl TryFrom<GroupMembershipRecord> for GroupMembershipRow {
+    type Error = GroupMembersRepositoryError;
+    fn try_from(r: GroupMembershipRecord) -> Result<Self, Self::Error> {
+        Ok(Self {
+            group_id: r.group_id.into(),
+            user_id: r.user_id.into(),
+            role: AppRole::from_db_str(&r.role)
+                .ok_or(GroupMembersRepositoryError::InvalidRole(r.role))?,
+            created_at: r.created_at,
+        })
+    }
+}
+
+#[derive(sqlx::FromRow)]
+struct GroupMembershipDetailRecord {
+    id: uuid::Uuid,
+    username: String,
+    email: Option<String>,
+    instance_role: String,
+    is_active: bool,
+    role: String,
+    created_at: DateTime<Utc>,
+}
+
+impl TryFrom<GroupMembershipDetailRecord> for GroupMembershipDetail {
+    type Error = GroupMembersRepositoryError;
+    fn try_from(r: GroupMembershipDetailRecord) -> Result<Self, Self::Error> {
+        Ok(Self {
+            user_id: r.id.into(),
+            username: r.username,
+            email: r.email,
+            instance_role: InstanceRole::from_db_str(&r.instance_role)
+                .ok_or(GroupMembersRepositoryError::InvalidRole(r.instance_role))?,
+            is_active: r.is_active,
+            role: AppRole::from_db_str(&r.role)
+                .ok_or(GroupMembersRepositoryError::InvalidRole(r.role))?,
+            created_at: r.created_at,
+        })
+    }
+}