fix: close the nine ways an unattended event loses photos or dies

Every one of these was found in the pre-event audit, verified against source, and
survives to production on the current main. Grouped by what actually goes wrong.

PHOTOS DISAPPEAR

* compression.rs no longer soft-deletes on a failed derivative. The guest got a
  201, watched the card appear, then watched it vanish — the row left v_feed,
  find_visible_media and BOTH keepsakes, while its bytes sat on disk for 14 days
  waiting for a cleanup nothing announced. No screen anywhere lists compression
  failures, so recovery meant hand-written SQL that also had to re-add the
  refunded quota. Now it does exactly what the ENOSPC arm beside it already did
  and documented as correct: keep the row, serve the original, retry on the next
  boot (bounded by derivative_attempts). `upload-deleted` is no longer emitted;
  `upload-processed` is, so the card re-renders instead of sitting on a
  placeholder.

* A 413 is now a reversible lock, so the blob survives. The quota moves — free
  disk falls, uploader count rises — so a guest goes over it having done nothing,
  and treating that as permanent meant a 400 MB video was pushed across cellular
  in full and THEN deleted from IndexedDB. Gone on both sides, and unrecoverable
  for an in-app camera capture that exists nowhere else.

* quota_limit_bytes gained a floor and a stable divisor. The ceiling used to
  decrease monotonically all evening; it now settles at max(uploaders,
  estimated_guest_count) — a config key that was seeded, validated in the admin
  whitelist, and read by no code at all. The floor is clamped to what the disk
  can actually back, so a full volume still yields zero rather than handing out
  an allowance it cannot honour.

* Because that floor gives up the aggregate guarantee the formula used to imply,
  uploads now check a hard 10 GB reserve first, independent of every quota
  toggle. postgres_data, media_data and exports_data share one filesystem: the
  end state was not a degraded feature, it was Postgres unable to write WAL.

THE ARCHIVE DISAPPEARS

* prune_superseded_archives runs only after the new generation lands. It ran
  before the preflight, reasoning the old archive was already unreachable — true
  of reachability, false of recoverability. An epoch is a value that can be
  rolled back; deleted bytes cannot. Any failed rebuild left the event with NO
  keepsake at all.

* The export preflight reserves the same 10 GB. `free < needed` authorised an
  export sized at exactly free, which ran for half an hour and landed the box at
  zero with the keepsake still unfinished.

THE APP DIES

* The feed reconcile re-reads the id set after its awaits instead of reusing one
  captured up to three round-trips earlier. The new-upload SSE handler prepends
  during exactly that window, so the row was both already present and absent from
  the stale set — prepended twice, and a duplicate key in a keyed {#each} throws
  in production, not just dev. The SSE handler and loadMore now dedupe too.

* Added routes/+error.svelte. Without it any uncaught error fell through to
  SvelteKit's unstyled English 500 with no reload control — inside a chromeless
  standalone PWA with no URL bar, for the rest of the evening.

THE OPERATOR IS LOCKED OUT

* admin_login verifies the password BEFORE charging the rate bucket, and a
  correct password is never throttled. The old order made this a denial of
  service against its own operator: every guest shares one NAT IP, the check ran
  first, so five requests a minute from any phone in the room kept the bucket
  full — and the escape hatch needed the admin session being blocked. A generous
  separate ceiling still bounds bcrypt CPU.

THE PROJECTOR DIES

* The preload budget is now strictly inside the dwell. At the 3s option the 4s
  budget could never land a commit on a slow uplink, so the wall froze on one
  photo while the queue drained silently behind it.

* The wake lock retries every 30s while visible, and the page says so on screen
  when the browser has no wake lock API. visibilitychange was the only retry
  trigger and a kiosk never changes visibility, so one refusal — iOS in Low Power
  Mode, say — was permanent.

* Caddy: /api/v1/upload/*/display joins the cacheable carve-out. The backend set
  max-age=300 on it and the blanket no-store silently replaced it, so a projector
  re-fetched a full-size JPEG per slide, ~2-4 GB over an evening on the uplink
  the guests are uploading over.

Also removes Upload::soft_delete, now unreferenced and an unscoped footgun next
to soft_delete_in_event.

Verified: 146/146 backend tests against a live Postgres, clippy clean, 51/51
vitest, svelte-check 0 errors, eslint clean, vite build, caddy validate, compose
YAML parse.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

frontend/src/lib/diashow/wakelock.ts

@@ -16,6 +16,19 @@ type WakeLock = { request: (t: string) => Promise<SentinelLike> };
 
 let sentinel: SentinelLike | null = null;
 let visibilityHandler: (() => void) | null = null;
+let retryTimer: ReturnType<typeof setInterval> | null = null;
+
+/**
+ * How often to retry while visible and lock-less.
+ *
+ * `visibilitychange` was the ONLY retry trigger, and a kiosk never changes visibility: the
+ * projector tab is opened once and left alone for eight hours. So a single refusal at startup
+ * was permanent. Refusal is not exotic either — iOS declines Screen Wake Lock outright in Low
+ * Power Mode, which is exactly the state a tablet that has been sitting on a table all
+ * afternoon is in. The symptom is the screen sleeping mid-party and someone having to walk
+ * over and tap it, repeatedly.
+ */
+const RETRY_INTERVAL_MS = 30_000;
 
 async function request(wakeLock: WakeLock): Promise<void> {
 	try {
@@ -33,9 +46,17 @@ async function request(wakeLock: WakeLock): Promise<void> {
 	}
 }
 
-export async function acquireWakeLock(): Promise<void> {
+/**
+ * Acquire the screen wake lock, and keep trying.
+ *
+ * Returns whether the API exists at all, so the caller can tell "the browser cannot do this,
+ * warn the operator" (Firefox, Safari < 16.4, most TV browsers) apart from "asked for, may
+ * still arrive". It deliberately does NOT report whether the first request succeeded — that
+ * answer goes stale immediately, and the retry loop below is what actually matters.
+ */
+export async function acquireWakeLock(): Promise<boolean> {
 	const wakeLock = (navigator as Navigator & { wakeLock?: WakeLock }).wakeLock;
-	if (!wakeLock) return;
+	if (!wakeLock) return false;
 	await request(wakeLock);
 
 	// Re-acquire when the page becomes visible again (the OS releases the lock
@@ -48,6 +69,17 @@ export async function acquireWakeLock(): Promise<void> {
 		};
 		document.addEventListener('visibilitychange', visibilityHandler);
 	}
+
+	// The kiosk case: visible, no lock, and no visibility change ever coming. Cheap enough to
+	// run all evening — it does nothing at all once a lock is held.
+	if (!retryTimer) {
+		retryTimer = setInterval(() => {
+			if (document.visibilityState === 'visible' && sentinel === null) {
+				void request(wakeLock);
+			}
+		}, RETRY_INTERVAL_MS);
+	}
+	return true;
 }
 
 export async function releaseWakeLock(): Promise<void> {
@@ -63,4 +95,8 @@ export async function releaseWakeLock(): Promise<void> {
 		document.removeEventListener('visibilitychange', visibilityHandler);
 		visibilityHandler = null;
 	}
+	if (retryTimer) {
+		clearInterval(retryTimer);
+		retryTimer = null;
+	}
 }