feat(block1): inventory walking skeleton + first quick-add slice

Stand up the Tanemaki monorepo and the first end-to-end vertical slice of
Block 1 (offline, encrypted inventory): add a seed → see it in a categorized,
searchable list → it persists → reopen and it's still there.

Architecture (state management like G1nkgo, adapted to Tane's reality):
- flutter_bloc (Cubit-first), but the encrypted Drift DB is the single source
  of truth; cubits stream from repositories (no hydrated_bloc/Hive, which would
  write plaintext at rest).
- get_it composition root; go_router; slang i18n (ES/EN, Weblate-friendly JSON).

Workspace & core:
- pub workspace: packages/commons_core (pure Dart) + apps/app_seeds (Flutter).
- commons_core primitives: UUIDv7 IdGen, Hybrid Logical Clock, Quantity value
  type (+ plant-aware QuantityKind), IdentityService root-seed stub.

Data & security:
- Drift schemaVersion=1 with all 10 Block-1 tables + common CRDT columns
  (HLC updated_at, last_author, tombstones); Movement append-only.
- SQLCipher via an injectable executor that refuses to open a plaintext DB;
  DB key + root seed in the OS keystore (separate secrets).
- Exported drift_schema_v1.json + migration scaffold.

Tests (near-TDD; nothing merges without tests):
- commons_core units (24), Drift migration test, "no plaintext at rest"
  security guard (runs where SQLCipher is present, skips otherwise),
  repository, widget, full quick-add flow, file-reopen persistence, and a
  no-hardcoded-strings i18n guard. GitLab CI: format + analyze + test + coverage.

Follow-on Block-1 stories (item detail/edit, species catalog, germination UI)
and all of Block 2 remain out of scope.

packages/commons_core/test/identity/identity_service_test.dart

@@ -0,0 +1,37 @@
+import 'dart:math';
+
+import 'package:commons_core/commons_core.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('IdentityService', () {
+    test('generates a 32-byte root seed', () {
+      final seed = IdentityService().generateRootSeed();
+      expect(seed.length, IdentityService.rootSeedLengthBytes);
+      expect(seed.length, 32);
+    });
+
+    test('two seeds from a secure RNG differ', () {
+      final service = IdentityService();
+      expect(service.generateRootSeed(), isNot(service.generateRootSeed()));
+    });
+
+    test('is reproducible with an injected seeded RNG (test-only)', () {
+      // `equals` does element-wise comparison on the byte lists.
+      final s1 = IdentityService(random: Random(1)).generateRootSeed();
+      final s2 = IdentityService(random: Random(1)).generateRootSeed();
+      expect(s1, equals(s2));
+    });
+  });
+
+  group('randomBytes', () {
+    test('returns the requested length', () {
+      expect(randomBytes(16).length, 16);
+      expect(randomBytes(0).length, 0);
+    });
+
+    test('rejects negative lengths', () {
+      expect(() => randomBytes(-1), throwsArgumentError);
+    });
+  });
+}