fix(user-flow): close offline-queue, export, session, ban & realtime gaps

Comprehensive user-flow review across guest/host/admin roles, then fixes with
e2e regression guards. Highlights:

- Offline upload queue auto-resumes on reconnect: network errors keep items
  pending (not error), 4xx are terminal (no infinite retry), quota exhaustion
  returns a distinct 413; queue cap + dedup.
- Export lifecycle: release atomically locks uploads; reopen invalidates and
  re-release regenerates the keepsake; workers claim their job atomically so a
  reopen->re-release can't corrupt the ZIP; startup re-spawns interrupted
  exports.
- Sessions slide on activity (no 30-day cliff); JWT expiry deferred to the
  revocable session row; sign-out-everywhere + revoke-on-PIN-reset.
- Ban always hides content (v_feed / find_visible_media / export filter
  is_banned) but stays a read-only ban per USER_JOURNEYS §10 — sessions are
  not revoked, read access + keepsake download preserved.
- Realtime: server-clock SSE delta cursor; event-closed/opened drive the UI
  live; feed_delta rate-limited; like returns {liked, like_count} to fix
  multi-device drift; lightbox live comments; diashow delta backfill.
- Forgotten-PIN in-app request flow; simultaneous same-name join returns 409;
  quota increment is transactional; operator floor.

Adds e2e/specs/10-flow-review/ (offline resume, export integrity, deterministic
anti-race guard) and updates existing specs for the new contracts.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/auth/jwt.rs

@@ -46,10 +46,20 @@ pub fn create_token(
 }
 
 pub fn verify_token(token: &str, secret: &str) -> Result<Claims, jsonwebtoken::errors::Error> {
+    // We deliberately do NOT enforce the JWT's own `exp`. The authoritative session
+    // lifetime lives in the `session` row (`expires_at > NOW()`), which SLIDES forward on
+    // every authenticated request (see `Session::touch_and_renew`). Enforcing the JWT's
+    // fixed +Nd `exp` here would hard-log-out an actively-used client on day N+1 even
+    // though its session was renewed — the "30-day cliff" from the review. With server-
+    // side sliding sessions, the token is a signature-checked bearer credential and its
+    // lifetime is revocable (logout / expiry / ban all delete the row), which is strictly
+    // stronger than a stateless non-revocable exp.
+    let mut validation = Validation::default();
+    validation.validate_exp = false;
     let data = jsonwebtoken::decode::<Claims>(
         token,
         &DecodingKey::from_secret(secret.as_bytes()),
-        &Validation::default(),
+        &validation,
     )?;
     Ok(data.claims)
 }