feat(web): session-row Rename menu action with a browser-owned dialog

The row menu's Rename item opens the same dialog pattern as workspace rename
(no client-side conflict rule; the host normalizes) and resolves through the
session face via ctx.sessions.binding. Assembled-app snapshot covers the
row-menu -> dialog -> unary-settle flow.

packages/client/ui-workspace/tests/workspace-browser.spec.tsx

@@ -55,6 +55,7 @@ function mount(overrides: Partial<WorkspaceBrowserProps> = {}) {
     actions: store.actions,
     startSession: vi.fn(),
     open: vi.fn(),
+    renameSession: vi.fn(async () => {}),
     renameWorkspace: vi.fn(async () => {}),
     deleteWorkspace: vi.fn(async () => {}),
     insertSessionBefore: vi.fn(async () => {}),