Add doc-service tests, AI category suggestions, LM Studio default

- pytest suite for doc-service: 20+ tests covering category CRUD,
  document upload/get/delete/patch, ownership isolation, category
  assignment, AI processing (mock), and live PDF tests (auto-skipped
  when tests/pdfs/ is empty)
- Minimal in-memory PDF builder in conftest so tests run without any
  fixture files; real PDFs can be dropped into tests/pdfs/ to activate
  live extraction tests
- AI prompt updated to return suggested_categories (2–5 short names)
- Frontend: SuggestionChip component in DocumentRow shows AI-suggested
  categories after processing; "Assign" links to an existing category,
  "Create & Assign" creates it first, ✕ dismisses locally
- Default AI provider changed to LM Studio at
  http://host.docker.internal:1234/v1 (host.docker.internal resolves
  to the macOS host from inside Docker Desktop)
- tests/pdfs/ directory tracked via .gitkeep; *.pdf excluded by .gitignore

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

changelog/2026-04-14_doc-service-tests-suggestions.md

@@ -0,0 +1,24 @@
+# 2026-04-14 — Doc-service tests, AI category suggestions, LM Studio default
+
+**Timestamp:** 2026-04-14T00:00:00+00:00
+
+## Summary
+
+Added pytest test suite for doc-service, updated the AI prompt to return suggested categories, wired up a suggestions UI in DocumentsPage (per-suggestion Accept/Create&Assign/Dismiss), changed the default AI provider to LM Studio at host.docker.internal:1234, and created a gitignored test PDF directory.
+
+## Files Added
+
+- `features/doc-service/tests/__init__.py`
+- `features/doc-service/tests/conftest.py` — SQLite in-memory DB, tmp DATA_DIR, mock AI provider, minimal+invoice PDF builders, real_pdfs fixture (auto-skips if no PDFs present)
+- `features/doc-service/tests/test_categories.py` — full CRUD + per-user isolation
+- `features/doc-service/tests/test_documents.py` — upload, list, get, status, delete, category assignment, AI processing integration, live PDF tests
+- `features/doc-service/tests/pdfs/.gitkeep` — tracked empty directory; drop PDFs here for live testing
+
+## Files Modified
+
+- `.gitignore` — ignore `features/doc-service/tests/pdfs/*.pdf`
+- `features/doc-service/pyproject.toml` — added `aiosqlite>=0.20` to dev deps
+- `features/doc-service/app/services/ai/base.py` — added `suggested_categories` to AI prompt (2–5 category names per document)
+- `features/doc-service/app/services/config_reader.py` — default provider changed to `lmstudio`; URLs changed to `host.docker.internal:1234/v1` (Docker→host resolution on macOS/Windows)
+- `backend/app/core/app_config.py` — default `LMStudioConfig.base_url` = `http://host.docker.internal:1234/v1`; default provider = `lmstudio`
+- `frontend/src/pages/DocumentsPage.tsx` — added `SuggestionChip` component and `suggested_categories` section in DocumentRow: checks if suggestion already exists as a user category, shows "Assign" (existing) or "Create & Assign" (new), dismiss removes from local state