feat(project-tool): multi-repo single-owner ownership + takeover (§7 M3)

Ports the M3 milestone from the superseded feat/hierarchies branch onto main's
evolved apply engine. A group node is authoritatively managed by at most one
project-root; `pic apply --dir` claims, conflicts, takes over, and (with
--prune) structurally reaps owned nodes.

- Migration 0066: `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; `pic plan --dir` surfaces
  ownership conflicts + structural-prune candidates read-only.
- Server: prepare_tree resolves ownership read-only (token folds each group's
  owner key, so a claim/takeover by another repo between plan and apply trips
  StateMoved). apply_tree upserts the project in-tx, claims unclaimed declared
  groups, and takes over owned ones under `--takeover`. --prune reaps
  owned-but-undeclared groups leaf-first (delete_group_tx 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.

Adaptation to main (which lacks the superseded branch's M2 declarative group
create/reparent): groups pre-exist, so ownership stamps existing declared
nodes rather than claim-on-create; the declarative attach-point is deferred.

Review fixes (adversarial pass, 3 findings, all closed):
- HIGH: an empty `[group]` node was claimed capability-free — require a
  baseline GroupScriptsWrite (editor) on every group apply node, so claiming
  ownership needs write authority (Ownership ⟂ RBAC).
- MEDIUM: structural prune would silently CASCADE a group's §11.6 shared
  collections + secrets (which postdate M3's original design). Guard: a prune
  candidate holding shared data/secrets is KEPT with a warning (plus its
  candidate ancestors, so a preserved child never aborts a parent delete).
- LOW: a corrupt `.picloud/project.json` silently re-minted a new key
  (orphaning ownership) — now fails loudly if the file exists but won't parse.

Tests: tests/ownership.rs (claim → conflict → takeover → flip; non-admin
takeover → 403; prune-owned-only; prune-refuses-to-cascade-shared-data);
format_conflicts + validate_project_key unit tests; schema golden reblessed.

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

crates/manager-core/tests/expected_schema.txt

@@ -318,6 +318,11 @@ 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
@@ -579,6 +584,7 @@ indexes on group_queue_messages:
   idx_group_queue_messages_group_collection: public.group_queue_messages USING btree (group_id, collection)
 
 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)
@@ -595,6 +601,10 @@ 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)
 
@@ -817,6 +827,7 @@ constraints on group_queue_messages:
   [PRIMARY KEY] group_queue_messages_pkey: PRIMARY KEY (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)
@@ -834,6 +845,10 @@ 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)
@@ -973,3 +988,4 @@ constraints on vars:
   0063: materialized unique
   0064: shared topic queue kinds
   0065: group queues
+  0066: owner project