Initial commit: opencode_bridge JupyterLab extension (Slices 1-3.5)

A JupyterLab extension that bridges the cell UI to a local OpenCode Serve
process. The extension is a dual package: a Python server extension
exposed under /opencode-bridge/*, plus a TypeScript frontend that
registers per-cell toolbars.

Backend (Python, tornado)
- Slice 1: config + auth + OpenCode HTTP client (tornado.httpclient,
  no aiohttp). 4 settings in schema/plugin.json (url, user, password,
  request timeout).
- Slice 2: handlers for /hello, /health, /providers, /edit.
- Slice 2.1 (correction): SessionManager with 1 notebook = 1 session
  mapping, async-safe via per-path locks, 404 recovery via invalidate().
  Two new endpoints: GET /sessions, DELETE /session?notebook=<path>.
- 32 pytest tests pass.

Frontend (TypeScript, JupyterLab 4.6)
- src/types.ts: CellContext, OpenCodeRequest/Response, OpenCodeSettings.
- src/context/cell_context.ts: extract CellContext from a CodeCell +
  its parent NotebookPanel, structured error collection.
- src/api/opencode_client.ts: callOpenCodeEdit, callOpenCodeProviders.
- src/components/opencode_cell_footer.ts: OpenCodeCellFooter Widget
  implementing ICellFooter with 3 buttons (optimize / fix / edit),
  resolved via this.parent instanceof CodeCell. NOT cellToolbar
  (does not exist in JL 4.6) and NOT Widget.findParent (removed in
  @lumino/widgets 2.x).
- src/components/opencode_cell_factory.ts: Cell.ContentFactory
  subclass returning the OpenCodeCellFooter.
- src/components/opencode_installer.ts: installOpenCodeEverywhere
  patches every notebook (existing + new) to use the custom factory.
- src/index.ts: registers the factory, loads settings, fetches
  /providers on activation and logs the list to the console.
- 23 jest tests pass (mocked JupyterLab boundary, pnpm path safe).

Settings
- 6 fields: 3 auth (url/user/password) + 1 timeout + 2 model selection
  (provider/model). Provider list is fetched at startup from
  /opencode-bridge/providers and printed to the browser console so
  users can copy values into Settings Editor.

Docs
- design.md: 6 sections covering architecture, UI flow, API contract,
  TS skeletons, session management (v0.2.1 correction), and
  provider/model selection (v0.2.2 addition).
- CLAUDE.md: agent guidance for working in this repo.
- TODO.md: remaining work for Slices 4-7 + v0.4+ backlog.

CI
- Gitea release workflow at .github/workflows/build.yml.
- Bark notification helper (non-fatal on failure).

Generated artefacts ignored: opencode_bridge/labextension/, _version.py,
*.tsbuildinfo, junit.xml, test.ipynb scratch notebook.

README.md

@@ -0,0 +1,49 @@
+# opencode_bridge
+
+[![Github Actions Status](http://101.43.40.124:3000/tao.chen/notebook-ai-extension.git/workflows/Build/badge.svg)](http://101.43.40.124:3000/tao.chen/notebook-ai-extension.git/actions/workflows/build.yml)
+
+A JupyterLab extension.
+
+This extension is composed of a Python package named `opencode_bridge`
+for the server extension and a NPM package named `opencode_bridge`
+for the frontend extension.
+
+## Requirements
+
+- JupyterLab >= 4.0.0
+
+## Install
+
+To install the extension, execute:
+
+```bash
+pip install opencode_bridge
+```
+
+## Uninstall
+
+To remove the extension, execute:
+
+```bash
+pip uninstall opencode_bridge
+```
+
+## Troubleshoot
+
+If you are seeing the frontend extension, but it is not working, check
+that the server extension is enabled:
+
+```bash
+jupyter server extension list
+```
+
+If the server extension is installed and enabled, but you are not seeing
+the frontend extension, check the frontend extension is installed:
+
+```bash
+jupyter labextension list
+```
+
+## Contributing
+
+If you would like to contribute to this extension, please refer to the [Contributing Guide](CONTRIBUTING.md).