fix(user-flow): persona-audit fixes — ban replay, locked-upload data loss, host UX, admin session

Follows the perf + security + user-flow work with a role/persona audit (guest, host,
admin, projector) and fixes across three review rounds. Highlights:

HIGH
- Ban now replays on reconnect. A ban isn't a soft-delete, and the `user-hidden` SSE has
  no replay, so a client that missed it (esp. the unattended diashow) kept cycling a
  banned user's slides. New `uploads_hidden_at` (migration 013) + `hidden_user_ids` in
  /feed/delta; feed + diashow evict those users. Applied even on a truncated delta.

MEDIUM
- Locked-upload data loss: a photo staged offline during a lock/release was purged as a
  terminal 4xx and lost when the host reopened. New reversible `uploads_locked` error code;
  the queue keeps the blob and auto-resumes on the `event-opened` SSE.
- Reopen after release now warns (ConfirmSheet) that it revokes the published keepsake.
- Host "forgotten-PIN" badge updates live (`pin-reset-requested` was broadcast but never
  in KNOWN_EVENTS / subscribed); host page also refetches on `pin-reset` so a two-host
  race can't hand out a conflicting PIN.
- Ban modal copy fixed (read-only ban, not "session ended"); Degradieren/Sperren/Entsperren
  hidden on peer-host rows for non-admins (they always 403'd).
- Host dashboard shows live keepsake generation progress / ready state + link to /export.
- Admin JWT moved to sessionStorage (§11.1) to bound exposure on shared devices.

Export generation guard (H1 from the prior round, hardened): per-(event,type) `release_seq`
(migration 012) with seq-guarded claim/finalize/mark_failed/update_progress, per-generation
temp/final paths, download follows `file_path`, prune only strictly-older generations.

LOW: diashow coalesces upload-processed (avoids self-rate-limit); event-closed reconciles
galleryReleased; /recover gains a forgot-PIN request + drops a stale cached PIN on 401;
delta `>=` tie-break + 429 retry; misc copy/labels.

Adds e2e: ban-replay, upload-lock-code, and rewrites export-reopen-rerelease with a
data-completeness test. Reconciles USER_JOURNEYS §9/§11.

Verified: cargo build clean, 40 unit tests, svelte-check 0 errors, 33 frontend unit
tests, 155 e2e passing on chromium-desktop.

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

backend/src/error.rs

@@ -6,6 +6,11 @@ pub enum AppError {
     BadRequest(String),
     Unauthorized(String),
     Forbidden(String),
+    /// Uploads are temporarily locked (event closed / gallery released). Distinct from
+    /// `Forbidden` so the client can tell this REVERSIBLE 403 apart from a permanent one
+    /// (banned user, quota): the queued blob is kept and retried if the host reopens,
+    /// instead of being purged like a genuinely-terminal rejection.
+    UploadsLocked(String),
     NotFound(String),
     Conflict(String),
     /// Second field: optional retry-after seconds to include in the response.
@@ -23,6 +28,7 @@ impl AppError {
             Self::BadRequest(_) => (StatusCode::BAD_REQUEST, "bad_request"),
             Self::Unauthorized(_) => (StatusCode::UNAUTHORIZED, "unauthorized"),
             Self::Forbidden(_) => (StatusCode::FORBIDDEN, "forbidden"),
+            Self::UploadsLocked(_) => (StatusCode::FORBIDDEN, "uploads_locked"),
             Self::NotFound(_) => (StatusCode::NOT_FOUND, "not_found"),
             Self::Conflict(_) => (StatusCode::CONFLICT, "conflict"),
             Self::TooManyRequests(..) => (StatusCode::TOO_MANY_REQUESTS, "too_many_requests"),
@@ -36,6 +42,7 @@ impl AppError {
             Self::BadRequest(msg)
             | Self::Unauthorized(msg)
             | Self::Forbidden(msg)
+            | Self::UploadsLocked(msg)
             | Self::NotFound(msg)
             | Self::Conflict(msg) => msg.clone(),
             Self::TooManyRequests(msg, _) => msg.clone(),