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/models/upload.rs

@@ -74,6 +74,22 @@ impl Upload {
         .await
     }
 
+    /// Like [`Self::find_by_id`] but also excludes uploads whose owner has been
+    /// ban-hidden (`user.uploads_hidden`). Used by the public original-file alias
+    /// so that moderation which hides a user's content from the feed/export also
+    /// stops their full-resolution originals from being pulled by UUID. Mirrors the
+    /// `uploads_hidden` filter that `v_feed` already applies to the feed.
+    pub async fn find_by_id_visible(pool: &PgPool, id: Uuid) -> Result<Option<Self>, sqlx::Error> {
+        sqlx::query_as::<_, Self>(
+            "SELECT up.* FROM upload up
+             JOIN \"user\" u ON u.id = up.user_id
+             WHERE up.id = $1 AND up.deleted_at IS NULL AND u.uploads_hidden = false",
+        )
+        .bind(id)
+        .fetch_optional(pool)
+        .await
+    }
+
     /// Event-scoped lookup used by host endpoints so a host of event A cannot
     /// reach uploads belonging to event B.
     pub async fn find_by_id_and_event(