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.

src/types.ts

@@ -0,0 +1,92 @@
+/**
+ * Shared types for the opencode-bridge frontend.
+ *
+ * These mirror the Python server's `CellContext` / `OpenCodeRequest` / `OpenCodeResponse`
+ * shapes in `opencode_bridge/routes.py`. Keep them in sync.
+ */
+
+export interface ErrorOutput {
+  ename: string;
+  evalue: string;
+  traceback: string[];
+}
+
+export interface CellContext {
+  notebookPath: string;
+  cellId: string;
+  language: string;
+  cellIndex: number;
+  totalCells: number;
+  source: string;
+  previousCode: string | null;
+  error: ErrorOutput | null;
+}
+
+export type OpenCodeMode = 'optimize' | 'fix' | 'edit';
+
+export interface OpenCodeRequest {
+  mode: OpenCodeMode;
+  prompt: string;
+  context: CellContext;
+  providerId?: string;
+  modelId?: string;
+}
+
+export interface OpenCodeSuccess {
+  ok: true;
+  mode: OpenCodeMode;
+  finalSource: string;
+  sessionId: string;
+  notebookPath: string;
+}
+
+export interface OpenCodeFailure {
+  ok: false;
+  error: string;
+}
+
+export type OpenCodeResponse = OpenCodeSuccess | OpenCodeFailure;
+
+/** Frontend view of the 4 schema/plugin.json fields. */
+export interface OpenCodeSettings {
+  opencodeServerUrl: string;
+  opencodeServerUser: string;
+  opencodeServerPassword: string;
+  requestTimeoutSeconds: number;
+  opencodeProvider: string;
+  opencodeModel: string;
+}
+
+export const DEFAULT_OPENCODE_SETTINGS: OpenCodeSettings = {
+  opencodeServerUrl: 'http://127.0.0.1:4096',
+  opencodeServerUser: 'opencode',
+  opencodeServerPassword: '',
+  requestTimeoutSeconds: 120,
+  opencodeProvider: '',
+  opencodeModel: '',
+};
+
+export function readOpenCodeSettings(composite: unknown): OpenCodeSettings {
+  const c = (composite ?? {}) as Partial<OpenCodeSettings>;
+  return {
+    opencodeServerUrl: c.opencodeServerUrl || DEFAULT_OPENCODE_SETTINGS.opencodeServerUrl,
+    opencodeServerUser: c.opencodeServerUser || DEFAULT_OPENCODE_SETTINGS.opencodeServerUser,
+    opencodeServerPassword: c.opencodeServerPassword || '',
+    requestTimeoutSeconds:
+      typeof c.requestTimeoutSeconds === 'number'
+        ? c.requestTimeoutSeconds
+        : DEFAULT_OPENCODE_SETTINGS.requestTimeoutSeconds,
+    opencodeProvider: c.opencodeProvider || '',
+    opencodeModel: c.opencodeModel || '',
+  };
+}
+
+/** Response from GET /opencode-bridge/providers. */
+export interface OpenCodeProvider {
+  id: string;
+  models: { id: string; [k: string]: unknown }[];
+}
+
+export interface OpenCodeProvidersResponse {
+  providers: OpenCodeProvider[];
+}