feat(modules): group-collection registry + group-KV storage schema (§11.6 C1)

Data layer for shared cross-app group collections (KV-only MVP), nothing wired
yet. Two migrations + two repos, modeled on the extension_points (0051) marker
and the kv_entries (0007) store:

- 0052_group_collections.sql: owner-polymorphic marker table declaring a
  collection name group-shared, with a `kind` discriminator (CHECK 'kv' for
  now; generalizes to docs/files/topics/queue later) and per-owner
  partial-unique (owner, LOWER(name), kind) indexes. CASCADE — a marker is
  config, not code.
- 0053_group_kv_entries.sql: the shared store, keyed by (group_id, collection,
  key) — NO app_id (a shared row belongs to the group). CASCADE on group delete
  (data dies with its group, like vars/secrets config; an app delete leaves it).
- group_collection_repo: list_for_owner, insert/delete_collection_tx, and the
  load-bearing resolve_owning_group — walks the reading app's chain
  (CHAIN_LEVELS_CTE) for the nearest ancestor group declaring the name
  (nearest-wins via ORDER BY depth LIMIT 1). That walk IS the isolation
  boundary; the join is on group_owner only.
- group_kv_repo: a near-clone of kv_repo keyed by group_id.

Schema snapshot re-blessed (53 migrations).

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

crates/manager-core/migrations/0052_group_collections.sql

@@ -0,0 +1,47 @@
+-- §11.6 (v1.2 Hierarchies): group-collection registry — shared cross-app data.
+--
+-- A row marks a collection NAME at a node as group-SHARED: every app in the
+-- owning group's subtree may read it (and, with an authenticated editor+,
+-- write it) via the explicit `kv::shared("name")` SDK handle. Resolution is
+-- nearest-ancestor-group-wins, walking the reading app's chain — that ancestry
+-- walk is the isolation boundary (a foreign app's chain never contains the
+-- owning group, so the name simply does not resolve). See docs §11.6.
+--
+-- This table holds only the MARKER (owner, name, kind) — the data itself lives
+-- in a per-kind storage table (`group_kv_entries`, 0053, for kind='kv'). It is
+-- pure declaration, structurally identical to an `extension_points` marker
+-- (0051). A marker is config, not code → ON DELETE CASCADE.
+--
+-- Ownership is polymorphic (mirrors vars/secrets/scripts/extension_points):
+-- exactly one of (app_id, group_id) is set. MVP authoring is restricted to
+-- GROUP owners at the manifest layer (an app-declared shared collection is
+-- degenerate — only that app would read it); the polymorphic shape keeps the
+-- owner-generic reconcile path uniform with the other inheritable kinds.
+--
+-- `kind` is the storage discriminator. Only 'kv' ships in the MVP; the column
+-- + CHECK exist now so docs/files/topics/queue slot in later without a
+-- migration, and so a future `docs` collection of the same name is a distinct
+-- row (the unique index covers `kind`).
+
+CREATE TABLE group_collections (
+    id          UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    group_id    UUID REFERENCES groups(id) ON DELETE CASCADE,
+    app_id      UUID REFERENCES apps(id) ON DELETE CASCADE,
+    CONSTRAINT group_collections_owner_exactly_one
+        CHECK ((group_id IS NULL) <> (app_id IS NULL)),
+    name        TEXT NOT NULL,
+    kind        TEXT NOT NULL DEFAULT 'kv' CHECK (kind IN ('kv')),
+    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at  TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+-- One marker per (owner, name, kind), case-insensitive. Partial because the
+-- owner is split across two nullable columns.
+CREATE UNIQUE INDEX group_collections_group_uidx
+    ON group_collections (group_id, LOWER(name), kind) WHERE group_id IS NOT NULL;
+CREATE UNIQUE INDEX group_collections_app_uidx
+    ON group_collections (app_id, LOWER(name), kind) WHERE app_id IS NOT NULL;
+
+-- Lookup indexes for the resolver's chain join + list-by-owner.
+CREATE INDEX group_collections_group_id_idx ON group_collections (group_id) WHERE group_id IS NOT NULL;
+CREATE INDEX group_collections_app_id_idx ON group_collections (app_id) WHERE app_id IS NOT NULL;