feat(manager-core,picloud): api_keys_api + deactivation cascade

* auth: generate_api_key() mints pic_<base32(32 bytes)>, splits the
  indexed 8-char prefix, and Argon2-hashes the body. Adds the
  data-encoding workspace dep for unpadded base32.
* api_keys_api: POST /api/v1/admin/api-keys (mint, returns raw_token
  exactly once), GET (caller's own, no raw), DELETE {id} (caller's
  own; 404 deliberately covers both 'missing' and 'not yours').
  Mint validation rejects bound keys carrying instance:* scopes (422).
* AdminsState gains the api keys repo; PATCH set_active(false) now
  expires every active key for that user alongside session wipe —
  Phase 3.5 deactivation symmetry.
* picloud lib wires PostgresApiKeyRepository through AuthDeps into
  AdminsState + ApiKeysState; api_keys_router merges into the
  guarded_admin layer.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Cargo.lock

@@ -408,6 +408,12 @@ dependencies = [
  "typenum",
 ]
 
+[[package]]
+name = "data-encoding"
+version = "2.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a4ae5f15dda3c708c0ade84bfee31ccab44a3da4f88015ed22f63732abe300c8"
+
 [[package]]
 name = "der"
 version = "0.7.10"
@@ -1374,6 +1380,7 @@ dependencies = [
  "axum",
  "base64",
  "chrono",
+ "data-encoding",
  "picloud-orchestrator-core",
  "picloud-shared",
  "rand 0.8.6",