fix(audit-followup): close regressions/gaps from the persona-audit re-review

Adversarial re-review of the persona-audit commit surfaced two HIGH regressions I'd
introduced plus MED/LOW gaps. All fixed:

HIGH
- Auth privilege escalation: reads are sessionStorage-first, but guest `setAuth` wrote only
  localStorage — a resident admin token shadowed a new guest login (guest ran as admin on a
  shared device). setAuth/setAdminAuth now DISPLACE the other store so exactly one identity
  is resident. Adds unit + e2e regression guards.
- Host dashboard: `exportGenerating` used `||`, so a one-half export failure stuck on
  "wird erstellt…" forever and never showed the re-release hint. Changed to `&&`.

MEDIUM
- Locked-upload auto-resume was unreliable (`event-opened` has no reconnect replay and SSE
  is down on non-feed pages) — now also resumes on `feed-delta`, which fires on every SSE
  reconnect.
- Queue-cap eviction could drop a recoverable locked item (parked as `error` with a live
  blob) — now evicts only `done`/`blocked`.
- Host page async-`onMount` leaked SSE handlers if unmounted mid-load — added a `destroyed`
  guard before registration.

LOW
- An unparseable 403 body now keeps the blob (reversible) instead of purging it.
- `refreshEventState` is sequence-guarded so a late close-refresh can't clobber a reopen.
- `/export/status` moved out of the all-or-nothing `reload()` so its failure can't blank the
  whole host dashboard.

Verified: svelte-check 0 errors, 36 frontend unit tests (incl. new displacement guards).

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

frontend/src/routes/host/+page.svelte

@@ -56,9 +56,12 @@
 	let exportReady = $derived(
 		exportInfo?.zip?.status === 'done' && exportInfo?.html?.status === 'done'
 	);
+	// The keepsake needs BOTH halves, so EITHER failing means the whole thing failed — use
+	// `&&` (not `||`), else a one-half failure stays stuck on "wird erstellt…" forever and the
+	// host never sees the "re-release" recovery hint.
 	let exportGenerating = $derived(
 		!!exportInfo?.released && !exportReady &&
-			(exportInfo?.zip?.status !== 'failed' || exportInfo?.html?.status !== 'failed')
+			exportInfo?.zip?.status !== 'failed' && exportInfo?.html?.status !== 'failed'
 	);
 	let exportProgress = $derived(
 		Math.min(exportInfo?.zip?.progress_pct ?? 0, exportInfo?.html?.progress_pct ?? 0)
@@ -148,6 +151,12 @@
 		}
 		await reload();
 
+		// The awaits above mean the component can already be destroyed by the time we get
+		// here (user navigated away mid-load). Svelte doesn't cancel an async onMount, so
+		// without this guard onDestroy would have run with an empty `sseOff` and we'd leak
+		// these handlers into the module-global SSE map forever.
+		if (destroyed) return;
+
 		// Live updates so the dashboard doesn't need a manual reload:
 		// - pin-reset-requested: a guest just asked for a reset → refresh the badge/list.
 		// - pin-reset: some host resolved a reset → drop it from the list (two-host race:
@@ -161,7 +170,9 @@
 		];
 	});
 
+	let destroyed = false;
 	onDestroy(() => {
+		destroyed = true;
 		for (const off of sseOff) off();
 	});
 
@@ -169,17 +180,20 @@
 		loading = true;
 		error = null;
 		try {
-			[event, users, pinResetRequests, exportInfo] = await Promise.all([
+			[event, users, pinResetRequests] = await Promise.all([
 				api.get<EventStatus>('/host/event'),
 				api.get<UserSummary[]>('/host/users'),
-				api.get<PinResetRequest[]>('/host/pin-reset-requests'),
-				api.get<ExportStatusDto>('/export/status')
+				api.get<PinResetRequest[]>('/host/pin-reset-requests')
 			]);
 		} catch (e: unknown) {
 			error = e instanceof Error ? e.message : 'Fehler beim Laden.';
 		} finally {
 			loading = false;
 		}
+		// Export status is a secondary widget — fetch it OUTSIDE the all-or-nothing block above
+		// (and error-swallowing) so a transient /export/status failure can't blank the whole
+		// dashboard (users, moderation, settings).
+		void refreshExportStatus();
 	}
 
 	/** Refetch just the pending PIN-reset requests (live badge; avoids a full-page reload). */