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/app/(site)/news/[...slug]/page.tsx

@@ -94,7 +94,7 @@ async function ArticlePage({
 	} catch {
 		logger.error("Public article lookup failed", { module: "news" });
 		return (
-			<main className="page-grid">
+			<section className="page-grid">
 				<ContentCard icon="📰" title={t("loadError")}>
 					<p role="alert">{t("loadError")}</p>
 					<a
@@ -104,7 +104,7 @@ async function ArticlePage({
 						{t("retry")}
 					</a>
 				</ContentCard>
-			</main>
+			</section>
 		);
 	}
 	if (!article) notFound();
@@ -159,7 +159,7 @@ async function ArticlePage({
 								: null;
 
 	return (
-		<main className="page-grid">
+		<section className="page-grid">
 			{comment === "posted" ? (
 				<div role="status" style={feedbackStyle("success")}>
 					{t("success.posted")}
@@ -196,7 +196,16 @@ async function ArticlePage({
 						src={article.image}
 						alt=""
 						decoding="async"
-						style={{ width: "100%", borderRadius: 10, margin: "0 0 1rem" }}
+						loading="eager"
+						// Reserve the box: an unbounded hero image shifts the whole
+						// article down once the bitmap decodes.
+						style={{
+							width: "100%",
+							aspectRatio: "16 / 9",
+							objectFit: "cover",
+							borderRadius: 10,
+							margin: "0 0 1rem",
+						}}
 					/>
 				) : null}
 				{/* Article body is rich HTML (atom uses TinyMCE) — sanitised server-side. */}
@@ -414,7 +423,7 @@ async function ArticlePage({
 					)}
 				</ContentCard>
 			</section>
-		</main>
+		</section>
 	);
 }
 

src/app/(site)/news/page.tsx

@@ -31,7 +31,7 @@ async function NewsPage({
 		`/news?${new URLSearchParams({ q: result?.search ?? params.q ?? "", order: result?.order ?? "newest", page: String(page) })}`;
 
 	return (
-		<main className="page-grid">
+		<section className="page-grid">
 			<ContentCard icon="📰" title={t("title")} subtitle={t("subtitle")} />
 
 			<ContentCard>
@@ -186,7 +186,7 @@ async function NewsPage({
 					</nav>
 				</ContentCard>
 			)}
-		</main>
+		</section>
 	);
 }