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.

opencode_bridge/config.py

@@ -0,0 +1,51 @@
+"""Configuration resolution for the opencode-bridge extension.
+
+Priority order (highest to lowest):
+  1. jupyter settings dict (from schema/plugin.json)
+  2. Environment variables (OPENCODE_BRIDGE_URL, _USER, _PASSWORD)
+  3. Built-in defaults
+"""
+from __future__ import annotations
+
+import os
+from typing import NamedTuple, Optional, Tuple
+
+ENV_URL = "OPENCODE_BRIDGE_URL"
+ENV_USER = "OPENCODE_BRIDGE_USER"
+ENV_PASSWORD = "OPENCODE_BRIDGE_PASSWORD"
+
+DEFAULT_URL = "http://127.0.0.1:4096"
+DEFAULT_USER = "opencode"
+DEFAULT_REQUEST_TIMEOUT = 120
+
+
+class OpenCodeConfig(NamedTuple):
+    url: str
+    user: str
+    password: str
+    request_timeout_seconds: int = DEFAULT_REQUEST_TIMEOUT
+
+    @property
+    def auth(self) -> Optional[Tuple[str, str]]:
+        """Return (user, password) for HTTP Basic Auth, or None if no password set."""
+        if not self.password:
+            return None
+        return (self.user, self.password)
+
+
+def resolve_config(jupyter_settings: dict) -> OpenCodeConfig:
+    """Resolve OpenCode connection config from jupyter settings + env + defaults."""
+    bridge = jupyter_settings.get("opencode_bridge", {}) or {}
+
+    return OpenCodeConfig(
+        url=bridge.get("opencodeServerUrl") or os.environ.get(ENV_URL) or DEFAULT_URL,
+        user=bridge.get("opencodeServerUser") or os.environ.get(ENV_USER) or DEFAULT_USER,
+        password=(
+            bridge.get("opencodeServerPassword")
+            or os.environ.get(ENV_PASSWORD)
+            or ""
+        ),
+        request_timeout_seconds=int(
+            bridge.get("requestTimeoutSeconds", DEFAULT_REQUEST_TIMEOUT)
+        ),
+    )