fix(audit): restore broken upload pipeline + role-based E2E audit fixes

A comprehensive role-based E2E audit (guest/host/admin, across browser
sessions) surfaced one critical and several smaller issues; this addresses
them and hardens the tests that missed them.

Critical
- The client upload pipeline was fully broken: the IndexedDB v1->v2 upgrade
  opened a *new* transaction inside the upgrade callback, which throws during
  a version-change transaction and aborted the whole upgrade, leaving the
  queue object store uncreated -- so no UI upload ever fired. Reuse the
  version-change transaction the callback provides, and bump the DB to v3 with
  a contains() guard so installs already corrupted by the shipped bug
  self-heal on next load. Re-enabled the previously-fixme'd UI upload E2E test.

High / Medium
- Event lock is uploads-only again: likes, comments and browsing stay open
  while the event is locked (USER_JOURNEYS 9.3 / FEATURES) -- it was wrongly
  freezing social interaction. Updated the event-lock spec accordingly.
- get_original now excludes soft-deleted and ban-hidden uploads, and direct
  /media/originals/** serving is blocked, so a hidden user's originals can no
  longer be pulled by UUID (all originals go through the checked alias).
- The upload handler reads the file field with an early-abort size cap chosen
  from the declared content-type, instead of buffering the entire body before
  the size check.

Low
- unban_user mirrors the ban role guard (a host can no longer unban a
  host/admin banned by an admin).
- reset_user_pin's UPDATE is event-scoped.
- Admin login returns and stores a real identity (user_id + display name)
  instead of a blank session.
- The host user list no longer renders target-actions (ban/promote/demote/PIN)
  on the caller's own row, where the backend always rejected them.
- /diashow gains a client-side auth guard like the other protected routes.
- The join page shows the event name via a new public GET /api/v1/event.

Verified: backend cargo build clean, frontend svelte-check 0 errors, full
Playwright E2E suite 144 passed / 1 skipped.

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

backend/src/handlers/host.rs

@@ -146,6 +146,26 @@ pub async fn unban_user(
     RequireHost(auth): RequireHost,
     Path(user_id): Path<Uuid>,
 ) -> Result<StatusCode, AppError> {
+    // Mirror the ban guard: a host may only lift bans on guests, never on hosts or
+    // admins. Without this a host could override an admin's ban of another host,
+    // which is asymmetric with `ban_user` and lets a host escalate a peer back in.
+    let target = sqlx::query_as::<_, (String,)>(
+        "SELECT role::text FROM \"user\" WHERE id = $1 AND event_id = $2",
+    )
+    .bind(user_id)
+    .bind(auth.event_id)
+    .fetch_optional(&state.pool)
+    .await?
+    .ok_or_else(|| AppError::NotFound("Benutzer nicht gefunden.".into()))?;
+
+    if target.0 == "admin"
+        || (target.0 == "host" && auth.role != crate::models::user::UserRole::Admin)
+    {
+        return Err(AppError::Forbidden(
+            "Du kannst diesen Benutzer nicht entsperren.".into(),
+        ));
+    }
+
     let result = sqlx::query(
         "UPDATE \"user\" SET is_banned = FALSE WHERE id = $1 AND event_id = $2",
     )
@@ -275,10 +295,11 @@ pub async fn reset_user_pin(
          SET recovery_pin_hash = $1,
              failed_pin_attempts = 0,
              pin_locked_until = NULL
-         WHERE id = $2",
+         WHERE id = $2 AND event_id = $3",
     )
     .bind(&pin_hash)
     .bind(user_id)
+    .bind(auth.event_id)
     .execute(&state.pool)
     .await?;