feat(hierarchies): multi-repo single-owner ownership + structural prune (M3)

§7 of the groups/project-tool design. A group node is now authoritatively
managed by exactly one project-root; `pic apply --dir` claims, conflicts,
takes over, and (with --prune) structurally reaps owned nodes.

- Migration 0052: `projects(id, key UNIQUE)` + promote the inert
  `groups.owner_project` (0047) to a real FK (ON DELETE SET NULL) + index.
- CLI mints a stable, gitignored project key in `.picloud/project.json`
  (`pic init`, or lazily on first tree plan/apply) and presents it on every
  tree request; `pic apply --dir --takeover` flag.
- Server: prepare_tree resolves ownership read-only (plan surfaces conflicts
  + prune candidates; token folds each group's owner key). apply_tree upserts
  the project in-tx, claims created groups on insert, reconciles existing-group
  ownership under the per-node advisory lock (first-commit-wins), and prunes
  owned-but-undeclared groups leaf-first (delete=RESTRICT, never another repo's
  or a UI-owned node).
- Authz (§7.4, ownership ⟂ RBAC): takeover requires GroupAdmin per contested
  node — enforced in authz_tree (pre-tx) AND re-verified in-tx at the ownership
  decision, so --force (which waives the staleness token) can't open a
  takeover-without-admin window. The attacker-supplied project key is
  length/charset-validated server-side.
- Tests: tests/ownership.rs (claim → conflict → takeover → flip; non-admin
  takeover → 403; prune-owned-only); format_conflicts unit test; schema golden
  reblessed. tree_shape M2 journey updated to reparent in-place (a fresh dir is
  now a distinct project and would correctly conflict).

Closes the M3 milestone; reviewed (4 findings: 1 authz-bypass via --force +
key validation + 2 LOW, all fixed). M4 (trigger/route templates) remains.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/manager-core/tests/expected_schema.txt

@@ -270,6 +270,11 @@ table: outbox
   claimed_by: text NULL
   created_at: timestamp with time zone NOT NULL default=now()
 
+table: projects
+  id: uuid NOT NULL default=gen_random_uuid()
+  key: text NOT NULL
+  created_at: timestamp with time zone NOT NULL default=now()
+
 table: pubsub_trigger_details
   trigger_id: uuid NOT NULL
   topic_pattern: text NOT NULL
@@ -492,6 +497,7 @@ indexes on group_members:
   group_members_user_id_idx: public.group_members USING btree (user_id)
 
 indexes on groups:
+  groups_owner_project_idx: public.groups USING btree (owner_project)
   groups_parent_id_idx: public.groups USING btree (parent_id)
   groups_pkey: public.groups USING btree (id)
   groups_slug_key: public.groups USING btree (slug)
@@ -508,6 +514,10 @@ indexes on outbox:
   idx_outbox_due: public.outbox USING btree (next_attempt_at) WHERE (claimed_at IS NULL)
   outbox_pkey: public.outbox USING btree (id)
 
+indexes on projects:
+  projects_key_key: public.projects USING btree (key)
+  projects_pkey: public.projects USING btree (id)
+
 indexes on pubsub_trigger_details:
   pubsub_trigger_details_pkey: public.pubsub_trigger_details USING btree (trigger_id)
 
@@ -695,6 +705,7 @@ constraints on group_members:
   [PRIMARY KEY] group_members_pkey: PRIMARY KEY (group_id, user_id)
 
 constraints on groups:
+  [FOREIGN KEY] groups_owner_project_fkey: FOREIGN KEY (owner_project) REFERENCES projects(id) ON DELETE SET NULL
   [FOREIGN KEY] groups_parent_id_fkey: FOREIGN KEY (parent_id) REFERENCES groups(id) ON DELETE RESTRICT
   [PRIMARY KEY] groups_pkey: PRIMARY KEY (id)
   [UNIQUE] groups_slug_key: UNIQUE (slug)
@@ -712,6 +723,10 @@ constraints on outbox:
   [FOREIGN KEY] outbox_app_id_fkey: FOREIGN KEY (app_id) REFERENCES apps(id) ON DELETE CASCADE
   [PRIMARY KEY] outbox_pkey: PRIMARY KEY (id)
 
+constraints on projects:
+  [PRIMARY KEY] projects_pkey: PRIMARY KEY (id)
+  [UNIQUE] projects_key_key: UNIQUE (key)
+
 constraints on pubsub_trigger_details:
   [FOREIGN KEY] pubsub_trigger_details_trigger_id_fkey: FOREIGN KEY (trigger_id) REFERENCES triggers(id) ON DELETE CASCADE
   [PRIMARY KEY] pubsub_trigger_details_pkey: PRIMARY KEY (trigger_id)
@@ -825,3 +840,4 @@ constraints on vars:
   0049: group secrets
   0050: group scripts
   0051: extension points
+  0052: owner project