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/routes/auth-helpers.ts

@@ -0,0 +1,48 @@
+import { eq } from "drizzle-orm";
+import { Router } from "express";
+import { z } from "zod";
+
+import { auth } from "../auth.js";
+import { db } from "../db/index.js";
+import { user } from "../db/schema/auth.js";
+
+// Public auth helpers that sit alongside Better Auth's own /api/auth handler.
+//
+// Better Auth's password-reset endpoint is keyed by email, but staff
+// provisioned by an admin sign in with a *username* (and may only have a
+// synthetic `username@slug.temetro.local` address). This lets them start a reset
+// by username: we resolve the username to its account, then hand off to the
+// normal reset flow (which emails a link if a provider is configured, or alerts
+// the clinic admins otherwise — see src/auth.ts sendResetPassword).
+export const authHelpersRouter = Router();
+
+const resetByUsernameSchema = z.object({
+  username: z.string().trim().min(1).max(64),
+  redirectTo: z.string().trim().max(2048).optional(),
+});
+
+// POST /api/auth-helpers/reset-by-username
+// Always responds 200 with a generic body — never reveals whether the username
+// exists (avoids account enumeration) and never echoes the resolved email.
+authHelpersRouter.post("/reset-by-username", async (req, res, next) => {
+  try {
+    const { username, redirectTo } = resetByUsernameSchema.parse(req.body);
+
+    const [account] = await db
+      .select({ email: user.email })
+      .from(user)
+      .where(eq(user.username, username.toLowerCase()))
+      .limit(1);
+
+    if (account?.email) {
+      // Reuse Better Auth's reset flow so the same dispatch/fallback logic runs.
+      await auth.api.requestPasswordReset({
+        body: { email: account.email, redirectTo },
+      });
+    }
+
+    res.json({ ok: true });
+  } catch (err) {
+    next(err);
+  }
+});