feat(projects): projects table + owner_project FK; ProjectId/Project types

First commit of §7 multi-repo ownership. A 'project' is a repo-root that
declaratively manages a slice of the shared group tree; each group node is
owned by exactly one project (single-owner-per-node). This lands the registry
+ shared types and wires the inert 0047 `owner_project` seam — no behavior
change yet (claim logic is the next commit).

- migration 0066: `projects` table (UUID pk, unique slug, name, created_by →
  admin_users ON DELETE SET NULL); `groups.owner_project` gains its FK →
  projects(id) ON DELETE SET NULL (un-claim, never cascade-destroy a tree) +
  an index.
- shared: `ProjectId` (id_type! macro) + `Project` struct; `Group` gains
  `owner_project: Option<ProjectId>`.
- group_repo: GROUP_COLS + the ancestors recursive-CTE term now carry
  `owner_project`, so `ancestors()` surfaces ownership for the nearest-claimed
  fold; GroupRow + From updated.
- schema snapshot re-blessed; /version schema assertion 65 → 66.

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

crates/shared/src/group.rs

@@ -11,7 +11,7 @@
 use chrono::{DateTime, Utc};
 use serde::{Deserialize, Serialize};
 
-use crate::GroupId;
+use crate::{GroupId, ProjectId};
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct Group {
@@ -26,6 +26,10 @@ pub struct Group {
     /// Per-subtree structure version, bumped on every structural mutation
     /// (reparent/rename/delete). Not an authz input.
     pub structure_version: i64,
+    /// §7 multi-repo ownership: the project that declaratively manages this
+    /// node, or `None` when the node is UI/API-owned (no manifest claims it).
+    /// Apps inherit ownership from their nearest claimed ancestor group.
+    pub owner_project: Option<ProjectId>,
     pub created_at: DateTime<Utc>,
     pub updated_at: DateTime<Utc>,
 }