feat(collab): nth-in-room colors, comment toolbar + drag + global hide, luminance chip text

- presence.ts: colors claimed by ARRIVAL ORDER — each client takes the lowest
  free palette slot (no birthday-problem hash collisions; the best palette
  colors go first; N ≤ palette-size editors always distinct). Coordination-
  free: claims ride awareness; simultaneous-join collisions converge (lower
  clientID keeps, the other re-claims), same-user tabs adopt one color,
  claims are sticky across eeschema sheet rebinds (skeletons reuse them).
  colorOf(userId) resolves live colors; comment pins/popovers follow it
  (offline authors fall back to the hash). +2 unit tests (verified live:
  alice=slot0, bob=slot1, roster/pins consistent).
- CommentLayer: single comment icon expanding into a horizontal bar — new
  comment · list · show/hide all (eye empties the GAL pin set + DOM targets;
  re-shown on new-comment/panel-jump). Pins are DRAGGABLE: live LWW anchor
  writes while dragging (peers + the GAL dot follow), nearest-item re-snap on
  drop, click-vs-drag by 4px threshold (verified live: drag synced to the
  peer tab exactly). Shared setThreadAnchor + controller moveThread/
  setPinsVisible/colorFor.
- collab_presence_style.h: chip text color by background luminance (dark on
  light chips, white on dark — BitmapText draws with the stroke color).
- comments/presence-roster e2e updated for the bar + passing; collab units
  56/56; shared 122/122; shared pointer bump.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CvqUd4QsJSGHN28aunJRTq

tests/web/comments.spec.ts

@@ -26,8 +26,11 @@ async function bootAs(page: Page, user: string): Promise<void> {
       intervals: [1000],
     })
     .toMatch(TITLE);
-  // The comment controls mount once the collab session + bridge are up.
-  await expect(page.getByTestId('comment-mode-toggle')).toBeVisible({ timeout: 30000 });
+  // The comment controls mount once the collab session + bridge are up; the
+  // action buttons live inside the expandable bar — open it for the test.
+  await expect(page.getByTestId('comment-bar-toggle')).toBeVisible({ timeout: 30000 });
+  await page.getByTestId('comment-bar-toggle').click();
+  await expect(page.getByTestId('comment-mode-toggle')).toBeVisible();
 }
 
 /** Delete every leftover thread from previous runs — comments PERSIST in the