feat(deploy): platform handoff — agent routing, persistence, docs cleanup

Agent routing:
- Remove !agent command and manual agent selection flow
- Registry auto-assigns agent from user_agents mapping (fallback: agents[0])
- provision_workspace_chat and !new both write agent_id to room_meta
- Reconciliation backfills agent_id from registry on cold start
- Fix duplicate agent_id block in auth.py

Deployment stability:
- Add bot-state named volume to persist lambda_matrix.db and matrix_store
- Fix docker-compose.prod.yml duplicate environment: key (was silently losing all Matrix credentials)
- Fix MATRIX_AGENT_REGISTRY_PATH to use absolute container path /app/config/...
- Add bot-state volume declaration to docker-compose.fullstack.yml

Docs and config:
- Rewrite README.md for platform handoff (deploy table, working commands only)
- Rewrite docs/matrix-prototype.md (remove stale commands and mock descriptions)
- Remove !save/!load/!context/!agent from help text and welcome message
- Add !clear, !list, !remove, !yes/!no to help text
- Clean up .env.example (remove Telegram token, internal vars, real URLs)
- Update config/matrix-agents.example.yaml with user_agents section and comments
- Add explanatory comment to Dockerfile for --ignore-requires-python
- Remove silent uv sync fallbacks in Dockerfile

Dockerfile

@@ -13,15 +13,17 @@ RUN pip install --no-cache-dir uv
 COPY pyproject.toml uv.lock* ./
 
 # Install project dependencies into the system environment.
-RUN uv sync --no-dev --no-install-project --frozen 2>/dev/null || uv sync --no-dev --no-install-project
+RUN uv sync --no-dev --no-install-project --frozen
 
 # Copy project source after dependency layers.
 COPY . .
 
-# Install the project itself and keep runtime dependencies in sync.
-RUN uv sync --no-dev --frozen 2>/dev/null || uv sync --no-dev
+# Install the project itself.
+RUN uv sync --no-dev --frozen
 
-# Install lambda_agent_api from the local source tree, bypassing its Python version guard.
+# Install lambda_agent_api from the vendored source tree.
+# --ignore-requires-python: the package declares python<3.12 but works fine on 3.11;
+# the guard exists for its own dev tooling, not the runtime API surface we use.
 RUN pip install --no-cache-dir --ignore-requires-python /app/external/platform-agent_api
 
 CMD ["python", "-m", "adapter.matrix.bot"]