Add FastAPI catalog backend (games/snapshots/diff) + tests

Modular-monolith backend over SQLAlchemy (SQLite by default, Postgres-ready
via DATABASE_URL). The full snapshot.json is stored verbatim; diffing reads it
back through the ams.diff engine, so the DB never mirrors the snapshot schema.

- ams.api.db/models/schemas/service : Game 1-N Snapshot, sha256-deduped upsert
- routes: POST/GET /games, POST/GET /snapshots (import, deduped), GET /diff
          (?old&new[&owner]) running compute_diff on stored snapshots, /health
- ams.api.importer : bulk CLI loader (python -m ams.api.importer --game ...)
- run: uvicorn ams.api.app:create_app --factory

11 tests pass (6 diff + 5 API via TestClient over the golden pair). Smoke-tested
live on uvicorn: import -> /snapshots -> /diff returns the BlooMoo deltas.

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

pyproject.toml

@@ -1,9 +1,28 @@
+[build-system]
+requires = ["setuptools>=68"]
+build-backend = "setuptools.build_meta"
+
 [project]
 name = "ams"
 version = "0.1.0"
-description = "Aidem Media engine-surface snapshot diffing (Piklib/BlooMoo)"
-requires-python = ">=3.9"
+description = "Aidem Media engine-surface snapshot diffing + catalog (Piklib/BlooMoo)"
+requires-python = ">=3.10"
 dependencies = []
 
+[project.optional-dependencies]
+api = [
+    "fastapi>=0.110",
+    "uvicorn[standard]>=0.27",
+    "sqlalchemy>=2.0",
+    "pydantic>=2.6",
+]
+dev = [
+    "pytest>=8",
+    "httpx>=0.27",
+]
+
+[tool.setuptools.packages.find]
+include = ["ams*"]
+
 [tool.pytest.ini_options]
 testpaths = ["tests"]