feat(hierarchies): extension points — opt-in dynamic module resolution (§5.5)

M1 of the remaining-hierarchies work. An extension point lets a PARENT/group
node opt a module name out of sealed lexical resolution: a parent script's
`import "x"` then resolves against the INHERITING app's module (with a declared
default body as fallback) instead of the parent's sealed chain — so each
descendant app supplies its own `x`. Only the declaring parent can open the
inversion; a descendant can never make a parent's sealed import dynamic or
hijack one (the "is this an extension point" decision keys on the importer's
trusted defining node, never a script-passed value).

Resolver (executor-core):
- `ModuleSource` gains `resolve_extension_point(origin, name)` and a
  chain-constrained `resolve_by_id(origin, id)`. The resolve seam checks for an
  ext point on the importer's chain first; on a hit it resolves against
  `App(cx.app_id)`, else the declared default, else ModuleNotFound. The Postgres
  query returns Some only when the NEAREST declaration of the name is an ext
  point (a peer/nearer concrete module shadows it). A group origin can't reach
  app-owned rows — the trust boundary holds. Cache stays id-keyed (no bleed).

Apply (manager-core, mirrors the `vars` pattern):
- migration 0051: owner-polymorphic `extension_points` table (group XOR app),
  optional `default_script_id` FK ON DELETE SET NULL, per-owner LOWER(name)
  unique indexes.
- Bundle/Plan/CurrentState gain extension_points; `diff_extension_points`
  (name-based, default change = Update), reconcile (upsert after scripts so the
  default resolves) + prune, `validate_bundle` (module-name shape; default must
  be a local module), `check_imports_resolve` (a declared/on-chain ext point
  satisfies an import), and the state_token fold. Writes gate on the
  script-write capability (AppWriteScript / GroupScriptsWrite).
- GET /apps|groups/{id}/extension-points so `pic pull` round-trips them — a
  re-applied pulled manifest is all-NoOp, so `--prune` can't silently drop one.

CLI: `[[extension_points]]` manifest table; plan/apply build + render; pull
exports them.

Tests: 5 resolver units (inversion, default fallback, no-provider error,
no-hijack of a sealed import, no cross-tenant cache bleed), 2 diff/state-token
units, 2 journeys (per-app resolution + default fallback via invoke; pull
round-trip). Schema golden re-blessed.

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

crates/manager-core/tests/expected_schema.txt

@@ -198,6 +198,15 @@ table: execution_logs
   app_id: uuid NOT NULL
   source: text NOT NULL default='http'::text
 
+table: extension_points
+  id: uuid NOT NULL default=gen_random_uuid()
+  group_id: uuid NULL
+  app_id: uuid NULL
+  name: text NOT NULL
+  default_script_id: uuid NULL
+  created_at: timestamp with time zone NOT NULL default=now()
+  updated_at: timestamp with time zone NOT NULL default=now()
+
 table: files
   app_id: uuid NOT NULL
   collection: text NOT NULL
@@ -463,6 +472,14 @@ indexes on execution_logs:
   execution_logs_pkey: public.execution_logs USING btree (id)
   execution_logs_script_id_created_at_idx: public.execution_logs USING btree (script_id, created_at DESC)
 
+indexes on extension_points:
+  extension_points_app_id_idx: public.extension_points USING btree (app_id) WHERE (app_id IS NOT NULL)
+  extension_points_app_uidx: public.extension_points USING btree (app_id, lower(name)) WHERE (app_id IS NOT NULL)
+  extension_points_default_script_idx: public.extension_points USING btree (default_script_id) WHERE (default_script_id IS NOT NULL)
+  extension_points_group_id_idx: public.extension_points USING btree (group_id) WHERE (group_id IS NOT NULL)
+  extension_points_group_uidx: public.extension_points USING btree (group_id, lower(name)) WHERE (group_id IS NOT NULL)
+  extension_points_pkey: public.extension_points USING btree (id)
+
 indexes on files:
   files_pkey: public.files USING btree (app_id, collection, id)
   idx_files_app_collection: public.files USING btree (app_id, collection)
@@ -656,6 +673,13 @@ constraints on execution_logs:
   [FOREIGN KEY] execution_logs_script_id_fkey: FOREIGN KEY (script_id) REFERENCES scripts(id) ON DELETE SET NULL
   [PRIMARY KEY] execution_logs_pkey: PRIMARY KEY (id)
 
+constraints on extension_points:
+  [CHECK] extension_points_owner_exactly_one: CHECK (((group_id IS NULL) <> (app_id IS NULL)))
+  [FOREIGN KEY] extension_points_app_id_fkey: FOREIGN KEY (app_id) REFERENCES apps(id) ON DELETE CASCADE
+  [FOREIGN KEY] extension_points_default_script_id_fkey: FOREIGN KEY (default_script_id) REFERENCES scripts(id) ON DELETE SET NULL
+  [FOREIGN KEY] extension_points_group_id_fkey: FOREIGN KEY (group_id) REFERENCES groups(id) ON DELETE CASCADE
+  [PRIMARY KEY] extension_points_pkey: PRIMARY KEY (id)
+
 constraints on files:
   [FOREIGN KEY] files_app_id_fkey: FOREIGN KEY (app_id) REFERENCES apps(id) ON DELETE CASCADE
   [PRIMARY KEY] files_pkey: PRIMARY KEY (app_id, collection, id)
@@ -800,3 +824,4 @@ constraints on vars:
   0048: vars
   0049: group secrets
   0050: group scripts
+  0051: extension points