feat: replace per-cell AI button with global floating panel

The per-cell toolbar AI button (OpenCodeCellActions) is removed. A
single round button is mounted on document.body at the bottom-right of
the JupyterLab shell; clicking it opens a floating panel containing
the same OpenCodeInlinePrompt widget. Clicking again closes it.

The panel resolves the active notebook from app.shell.currentWidget
at open time and re-resolves it whenever currentChanged fires while
the panel is open. The active cell (used by the 📋 插入单元格内容,
↪ Insert, and ⟳ Replace cell actions) is resolved via a new
getActiveCell callback in OpenCodeInlinePrompt, decoupling the prompt
itself from any specific CodeCell instance.

Files:
- src/components/opencode_floating_panel.ts (new) — global panel
- src/components/opencode_cell_actions.ts (deleted) — logic moved up
- src/components/opencode_inline_prompt.ts — getActiveCell option
- src/index.ts — wire floating panel, drop toolbar factory
- style/base.css — .opencode-floating-* styles
- src/__tests__/opencode_floating_panel.spec.ts — new tests (renamed)

All existing functionality preserved: multi-session UI, SSE
streaming, permission/question interaction, history reload.

src/index.ts

@@ -3,74 +3,56 @@ import {
   JupyterFrontEndPlugin
 } from '@jupyterlab/application';
 
-import { IToolbarWidgetRegistry } from '@jupyterlab/apputils';
-import { Cell, CodeCell } from '@jupyterlab/cells';
 import { Widget } from '@lumino/widgets';
 
-import {
-  OpenCodeCellActions,
-  setOpenCodeProviders,
-  setOpenCodeServerSettings
-} from './components/opencode_cell_actions';
+import { OpenCodeFloatingPanel } from './components/opencode_floating_panel';
 import { requestAPI } from './request';
 import { callOpenCodeProviders } from './api/opencode_client';
 
 /**
  * Initialization data for the opencode_bridge extension.
  *
- * v3-final: no JupyterLab plugin settings. Connection config is read from
- * environment variables by the server extension; the model is picked
- * dynamically in the inline prompt.
+ * v5-floating: the per-cell AI button is gone. A single
+ * OpenCodeFloatingPanel is attached to document.body and operates
+ * against the JupyterLab shell's currently-active notebook. The model
+ * is picked dynamically in the inline prompt.
  */
 const plugin: JupyterFrontEndPlugin<void> = {
   id: 'opencode_bridge:plugin',
   description: 'A JupyterLab extension bridging the UI to OpenCode Serve.',
   autoStart: true,
-  optional: [IToolbarWidgetRegistry],
-  activate: (
-    app: JupyterFrontEnd,
-    toolbarRegistry: IToolbarWidgetRegistry | null
-  ) => {
+  activate: (app: JupyterFrontEnd) => {
     console.log('JupyterLab extension opencode_bridge is activated!');
 
-    // Push the Jupyter server settings into the actions module so that
-    // callOpenCodeEdit can build the right base URL.
-    setOpenCodeServerSettings(app.serviceManager.serverSettings);
+    // Mount the floating AI button on the body. The panel itself is
+    // hidden until the user clicks the button.
+    const floating = new OpenCodeFloatingPanel({
+      app,
+      serverSettings: app.serviceManager.serverSettings,
+      providers: null
+    });
+    Widget.attach(floating, document.body);
 
-    // Register the per-cell AI actions into the native Cell toolbar
-    // (top-right of the active cell, next to move up/down). Non-code
-    // cells get an empty widget so they show no AI buttons.
-    if (toolbarRegistry) {
-      toolbarRegistry.addFactory<Cell>(
-        'Cell',
-        'opencode-cell-actions',
-        (cell: Cell) => {
-          if (cell instanceof CodeCell) {
-            return new OpenCodeCellActions(cell);
-          }
-          return new Widget();
-        }
-      );
-    }
-
-    // Fetch available providers once at activation and cache them for the
-    // inline prompt's model picker. Failure is non-fatal (the picker hides).
+    // Fetch available providers once at activation and cache them for
+    // the inline prompt's model picker. Failure is non-fatal (the
+    // picker hides). Also push the payload into the floating panel so
+    // the prompt can render selects without an extra round trip.
     void callOpenCodeProviders(app.serviceManager.serverSettings)
       .then(data => {
-        setOpenCodeProviders(data);
+        floating.setProviders(data);
         const lines: string[] = [
           '[opencode_bridge] Available OpenCode providers:'
         ];
         for (const p of data.providers) {
-          const models = Object.values(p.models).map(m => m.id).join(', ');
+          const models = Object.values(p.models)
+            .map(m => m.id)
+            .join(', ');
           lines.push(`  - ${p.id}: ${models || '(no models)'}`);
         }
-        // eslint-disable-next-line no-console
         console.log(lines.join('\n'));
       })
       .catch(reason => {
-        // eslint-disable-next-line no-console
-+        console.warn(
+        console.warn(
           '[opencode_bridge] Could not fetch providers (is the opencode-bridge server extension enabled and opencode serve running?):',
           reason
         );