feat: harden atoms-nexst against review findings (37 items)

Second review pass covering security, performance, admin tooling and the
public/room flows. All HIGH and MEDIUM findings from the audit are resolved;
nothing in this commit changes the visible feature set.

Authentication & session security
- CSP is now set on the request headers in the proxy, which is what Next.js
  uses to derive the render nonce, so the nonce is effective.
- 2FA: an already-enabled user cannot re-enroll, the setup endpoint is
  rate-limited per account, and confirmed codes are persisted so the second
  secret no longer silently never applies.
- Password reset revokes the ticket, authTicket and all personal access
  tokens, and bumps the token version so existing sessions die. The same
  revocation is now wired into the staff-side password reset.
- /reset and /verify return a stable error code instead of raw text; the
  mail lookups are ordered by id so duplicates cannot vary between runs.
- Resending the verification mail gets a per-address cooldown on top of the
  per-user limit.
- Issue API tokens with the narrower radio/ticket ability set instead of "*".

Authorization & input handling
- Mid-rank staff can no longer keep dynamically granted non-view admin.*
  permissions: existing grants are revoked by migration and the grant lookup
  is restricted to "%.view". Rank guards use the dynamic super-admin check.
- Alerting a user is permission-checked and audited like the other tools.
- Material mutations (giveCredits/giveDuckets/giveDiamonds, the admin user
  actions route, bulk user actions) are capped and rank-guarded, and bulk
  ids are bounded.
- updateRoom / updateRoomItem write through a field allowlist, and items
  may only be edited through their own room.
- Classnames reaching the filesystem are validated before use so a crafted
  value cannot escape the asset directories.
- The word filter now also covers offline mails, guild forum threads and
  replies, and user mottos.
- Media uploads are validated by magic bytes, /api/media requires the page
  edit permission, APP_URL must be configured once mail is enabled, and the
  diagnostics error route checks the fetch site header.

Admin tooling
- Secret settings render masked and cannot be overwritten with a blank or
  an arbitrary raw key; radio credentials are new password inputs.
- Commandocentrum balance changes are audited.
- Admin list pagination reads the caller's per-page instead of the max, and
  the log exporter caps offset and search length.

Performance
- Catalog translations are cached per module, with a cheap revision hash;
  the public online count uses a stale window instead of hammering the DB.
- The cache warmup now primes the payload the home route actually reads.
- TopHeader batches its queries into one round trip, and LCP avatars load
  eagerly.
- motion/react and sonner are no longer part of the root layout; the nav
  dropdown and mobile nav panels are lazy client chunks. Anonymous visitors
  again get the navigation chrome, and public pages get an edge cacheable
  response.

Accessibility
- Nested <main> elements in phase pages became <section>; the page entrance
  and route progress animations are pure CSS that respect reduced motion.

src/lib/services/setting-secrets.ts

@@ -0,0 +1,28 @@
+/** Setting keys whose value must never be sent to the browser. */
+const SECRET_SETTING_KEYS = new Set([
+	"turnstile_secret",
+	"recaptcha_secret",
+	"hcaptcha_secret",
+	"radio_azurecast_api_key",
+	"radio_sambroadcaster_password",
+	"radio_virtual_dj_password",
+	"radio_discord_webhook_url",
+	"gitea_token",
+]);
+
+/**
+ * A key is a secret when it is explicitly listed above, or when its name alone
+ * says so (`*_secret`, `*_password`, `*_api_key`, ...). Used by the settings UI
+ * to avoid shipping credentials in the RSC payload, and by the write actions to
+ * keep "blank means keep the stored value" semantics instead of wiping secrets.
+ */
+export function isSecretSettingKey(key: string): boolean {
+	const lower = key.toLowerCase();
+	if (SECRET_SETTING_KEYS.has(lower)) return true;
+	return /(^|_)(secret|password|passwd|token|api_?key|private_?key|credential)$/.test(
+		lower,
+	);
+}
+
+/** Replace a secret with a marker for UI rendering. */
+export const SECRET_PLACEHOLDER = "••••••••";