feat: upgrade to qwen3.5, self-hosted Gitea CI, optimize Docker image

Model upgrade:
- qwen2.5:14b → qwen3.5:latest across config, tools, and docs
- Added qwen3.5 to multimodal model registry

Self-hosted Gitea CI:
- .gitea/workflows/tests.yml: lint + test jobs via act_runner
- Unified Dockerfile: pre-baked deps from poetry.lock for fast CI
- sitepackages=true in tox for ~2s dep resolution (was ~40s)
- OLLAMA_URL set to dead port in CI to prevent real LLM calls

Test isolation fixes:
- Smoke test fixture mocks create_timmy (was hitting real Ollama)
- WebSocket sends initial_state before joining broadcast pool (race fix)
- Tests use settings.ollama_model/url instead of hardcoded values
- skip_ci marker for Ollama-dependent tests, excluded in CI tox envs

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

.env.example

@@ -14,8 +14,8 @@
 # In production (docker-compose.prod.yml), this is set to http://ollama:11434 automatically.
 # OLLAMA_URL=http://localhost:11434
 
-# LLM model to use via Ollama (default: qwen2.5:14b)
-# OLLAMA_MODEL=qwen2.5:14b
+# LLM model to use via Ollama (default: qwen3.5:latest)
+# OLLAMA_MODEL=qwen3.5:latest
 
 # Enable FastAPI interactive docs at /docs and /redoc (default: false)
 # DEBUG=true