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/messages/cs.json

@@ -815,7 +815,8 @@
 			"confirm": "Potvrďte",
 			"enableIntro": "Přidejte druhou vrstvu zabezpečení pomocí ověřovací aplikace.",
 			"enable": "Povolit 2FA",
-			"rateLimit": "Too many attempts. Please wait before trying again."
+			"rateLimit": "Too many attempts. Please wait before trying again.",
+			"alreadyEnabled": "Dvoufaktorové ověřování je už zapnuté. Pokud ho chcete nastavit znovu, nejprve ho vypněte."
 		},
 		"title": "Propojené účty",
 		"subtitle": "Propojte sociální účet a přihlaste se jedním kliknutím",
@@ -849,7 +850,8 @@
 			"showPassword": "Zobrazit",
 			"hidePassword": "Skrýt",
 			"registeredSuccess": "Úter vytvořen — zkontrolujte svou schránku a najděte ověřovací odkaz, poté se přihlaste.",
-			"verifyEmailCta": "Vyžádat nový ověřovací odkaz"
+			"verifyEmailCta": "Vyžádat nový ověřovací odkaz",
+			"passwordChanged": "Vaše heslo bylo změněno. Přihlaste se novým heslem."
 		},
 		"register": {
 			"title": "Vytvořit účet",
@@ -924,7 +926,8 @@
 			"emailPlaceholder": "Váš email",
 			"sendResetLink": "Odeslat odkaz na reset",
 			"backToLogin": "Zpět k přihlášení",
-			"errorCaptcha": "Captcha verification failed. Please try again."
+			"errorCaptcha": "Captcha verification failed. Please try again.",
+			"sendAnotherLink": "Odeslat další odkaz"
 		},
 		"reset": {
 			"title": "Nastavte nové heslo",
@@ -933,7 +936,9 @@
 			"resetPassword": "Obnovit heslo",
 			"backToLogin": "Zpět k přihlášení",
 			"passwordMinLength": "Heslo musí mít alespoň 12 znaků",
-			"tooManyAttempts": "Příliš mnoho pokusů — zkuste to později"
+			"tooManyAttempts": "Příliš mnoho pokusů — zkuste to později",
+			"invalidLink": "Tento odkaz pro obnovu je neplatný nebo vypršel. Vyžádejte si nový.",
+			"failed": "Heslo nebylo možné obnovit. Zkuste to prosím znovu."
 		},
 		"verify": {
 			"verifiedTitle": "Vše je připraveno",