test: add unit tests for all 10 routers (92 total)

New test files:
- test_conversations.py — list/create/get/update/delete/delete-all, admin enforcement
- test_presets.py — list/create/update/delete, default preset protection
- test_profile.py — get/update/default, length validation
- test_models_router.py — list/ps/show/stats/search-status, connect errors
- test_completions.py — API key auth, FIM passthrough, streaming/blocking, errors
- test_search_route.py — explicit search flow, no results, stream errors
- test_memories.py — edit/search/stats endpoints, validation, admin enforcement

Update AGENTS.md with full test file coverage table and README.md

README.md

@@ -19,6 +19,7 @@ Developer wiki: [docs/wiki/Home.md](docs/wiki/Home.md)
 - **All 8 test files fixed** — rewired imports after the modular refactor; all 26 tests pass
 - **Origin check extended to all API methods** — GET/HEAD/OPTIONS requests no longer bypass origin checking (was limited to POST/PUT/DELETE/PATCH)
 - **Missing headers now rejected** — `origin_allowed()` returns `False` when both `Origin` and `Referer` are absent, closing the CSRF read gap for script-initiated requests
+- **Full router test coverage** — 7 new test files added: `test_conversations.py`, `test_presets.py`, `test_profile.py`, `test_models_router.py`, `test_completions.py`, `test_search_route.py`, `test_memories.py`; all 10 routers now have dedicated unit tests (92 total, up from 26)
 
 ## Features