feat: username reset, system-message UX, meetings polish, sidebar identity

- auth: forgot-password now has Email/Username tabs; new public
  /api/auth-helpers/reset-by-username resolves a username and hands off to the
  existing reset flow (real email or admin-notify fallback)
- messages: conversations expose isSystem; System notices are read-only (no
  composer, no call button) and styled distinctly (shield icon + badge)
- meetings: compact, larger control bar; self tile shows real initials and an
  avatar (not black) when the camera is off; delete-room UI with confirm
- sidebar: username-only accounts show @username instead of a synthetic email

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/index.ts

@@ -9,6 +9,7 @@ import { env } from "./env.js";
 import { errorHandler, notFound } from "./middleware/error.js";
 import { initRealtime } from "./realtime.js";
 import { activityRouter } from "./routes/activity.js";
+import { authHelpersRouter } from "./routes/auth-helpers.js";
 import { aiRouter } from "./routes/ai.js";
 import { analyticsRouter } from "./routes/analytics.js";
 import { attachmentsRouter } from "./routes/attachments.js";
@@ -86,6 +87,7 @@ app.use("/api/ai", aiRouter);
 app.use("/api/chat", chatRouter);
 app.use("/api/integrations", integrationsRouter);
 app.use("/api/portal", portalRouter);
+app.use("/api/auth-helpers", authHelpersRouter);
 
 app.use(notFound);
 app.use(errorHandler);