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/manager-core/src/group_repo.rs

@@ -105,8 +105,8 @@ impl PostgresGroupRepository {
     }
 }
 
-const GROUP_COLS: &str =
-    "id, parent_id, slug, name, description, structure_version, created_at, updated_at";
+const GROUP_COLS: &str = "id, parent_id, slug, name, description, structure_version, created_at, \
+     updated_at, owner_project";
 
 #[async_trait]
 impl GroupRepository for PostgresGroupRepository {
@@ -157,7 +157,8 @@ impl GroupRepository for PostgresGroupRepository {
                  SELECT {GROUP_COLS}, 0 AS depth FROM groups WHERE id = $1
                UNION ALL
                  SELECT g.id, g.parent_id, g.slug, g.name, g.description, \
-                        g.structure_version, g.created_at, g.updated_at, c.depth + 1 \
+                        g.structure_version, g.created_at, g.updated_at, g.owner_project, \
+                        c.depth + 1 \
                  FROM groups g JOIN chain c ON g.id = c.parent_id \
                  WHERE c.depth < 64
              )
@@ -349,6 +350,7 @@ struct GroupRow {
     structure_version: i64,
     created_at: chrono::DateTime<chrono::Utc>,
     updated_at: chrono::DateTime<chrono::Utc>,
+    owner_project: Option<Uuid>,
 }
 
 impl From<GroupRow> for Group {
@@ -360,6 +362,7 @@ impl From<GroupRow> for Group {
             name: r.name,
             description: r.description,
             structure_version: r.structure_version,
+            owner_project: r.owner_project.map(Into::into),
             created_at: r.created_at,
             updated_at: r.updated_at,
         }