collab-presence 0010: unified draggable overlay menu

One circular FAB (peer-count badge) replaces the top-right overlay row:
draggable anywhere (pointer capture, 4px click-vs-drag threshold — the
comment-pin pattern), position persisted in localStorage, panel opens
toward screen center and stacks composable sections — roster, source chip,
view-only pill, follow row, comments, chrome toggle. Renders at z-50 above
everything (decided: covers wx dialogs; trivially dismissed via click-away/
Esc/drag). CommentLayer portals its bar + list panel into the menu's
comments slot; pins/popovers/composer/click-catcher stay canvas-anchored.
The FAB is the chrome-hidden survivor. e2e specs updated with an
openOverlayMenu helper (panel is closed by default, click-away closes it).

NOTE: Playwright suites updated but not executed here (no local WASM
artifacts) — verify on CI / next session.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01A42xfPFNdfsUt9eowkC9eM

tests/web/follow.spec.ts

@@ -1,4 +1,5 @@
 import { test, expect, type Page } from '@playwright/test';
+import { openOverlayMenu } from './overlay-menu';
 
 /**
  * Follow-user e2e (collab-presence 0008): two tabs on the demo BOARD share
@@ -81,7 +82,9 @@ test('B follows A: viewport mirrors, then local input breaks the follow', async
     })
     .toBe(true);
 
-  // B sees alice in the roster and clicks her avatar → follow.
+  // B sees alice in the roster (inside the overlay menu, 0010) and clicks
+  // her avatar → follow.
+  await openOverlayMenu(b);
   const avatar = b.locator('[data-presence-user="alice"]');
   await expect(avatar).toBeVisible({ timeout: 30000 });
   await avatar.click();