feat(secrets): group-owned, env-scoped secrets + inherited resolution

Migration 0049 reshapes `secrets` to the same polymorphic-owner contract
as `vars` (0048): a secret is owned by an app XOR an ancestor group,
carries an `environment_scope`, and the old PK `(app_id, name)` becomes
two partial-unique indexes `(owner, environment_scope, name)`. Existing
rows backfill to `app_id` + scope `'*'`; the v1 AAD does NOT include the
scope, so every current ciphertext keeps decrypting byte-for-byte.

`SecretsRepo` is generalised to be owner+scope keyed (`SecretOwner` moves
down from `secrets_service` and is re-exported for path stability). The
SDK read path now goes through `SecretsRepo::resolve`, which reuses the
shared `CHAIN_LEVELS_CTE` to walk app→ancestor-group→root, env-filters,
and takes the nearest level (`@E` beating `*` within a level) — returning
the winning owner so the value is decrypted under the AAD it was sealed
with. Runtime injection stays anchored to `cx.app_id`: an app only ever
resolves its own and its ancestors' secrets.

All callers updated to owner+scope (`SecretOwner::App(_)`, scope `'*'`):
the app-secrets admin API, the SDK service, and the apply email-secret
path. The 21 secrets unit tests (incl. the app/group AAD-disjointness and
cross-row swap proofs) stay green; the chain-walk was live-verified
against Postgres (nearest-wins + env-filter). Admin API for group secrets
and the masked-read endpoint land next (Step E).

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

crates/manager-core/src/lib.rs

@@ -204,7 +204,7 @@ pub use route_repo::{NewRoute, PostgresRouteRepository, RouteRepository};
 pub use sandbox::{CeilingError, SandboxCeiling};
 pub use secrets_api::{secrets_router, SecretsApiError, SecretsState};
 pub use secrets_repo::{
-    PostgresSecretsRepo, SecretMeta, SecretsMetaPage, SecretsNamePage, SecretsRepo,
+    PostgresSecretsRepo, ResolvedSecret, SecretMeta, SecretsMetaPage, SecretsNamePage, SecretsRepo,
     SecretsRepoError, StoredSecret,
 };
 pub use secrets_service::{