tests: fix suite-wide collection and failures

- config: switch Settings to ConfigDict(extra='ignore') so extra env vars
  (spoonacular_api_key, SWIFTLY_BEARER_TOKEN) don't crash import.
  Remove deprecated class Config.
- email: wrap SendGrid imports in try/except so the module loads without
  the optional dependency. Update test_email_backend to patch Mail/RepyTo.
- planner_select: default PlannerConfig.set_size=21 (3 meals/day × 7) is
  way too large for the unit test assertion that checks 3-recipe diversity.
  Introduced _CFG_3 with set_size=3 and applied to all tests.
- Delete stale test_matcher.py importing removed functions.

Full suite: 46 passed, 74 skipped (Postgres), 0 failed, 120 collected.

graphify-out/cache/ef69cca14d5c9cda29516aad9acc8fbdb405b5ca64d9fa3c8dfc8dd9960be7c7.json

@@ -0,0 +1 @@
+{"nodes": [{"id": "backend_app_scheduler_init_py", "label": "__init__.py", "file_type": "code", "source_file": "backend/app/scheduler/__init__.py", "source_location": "L1"}], "edges": [], "raw_calls": []}