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>

frontend/src/routes/admin/login/+page.svelte

@@ -18,9 +18,14 @@
 		loading = true;
 		error = '';
 		try {
-			const res = await api.post<{ jwt: string }>('/admin/login', { password });
-			// Admin sessions have no PIN; pass null so setAuth doesn't overwrite a guest PIN
-			setAuth(res.jwt, null, '');
+			const res = await api.post<{ jwt: string; user_id: string; display_name: string }>(
+				'/admin/login',
+				{ password }
+			);
+			// Admin sessions have no PIN; pass null so setAuth doesn't overwrite a guest PIN.
+			// Persist the real user id + name so the admin has an identity (own-post
+			// affordances on the feed, a name on the Account page rather than "Unbekannt").
+			setAuth(res.jwt, null, res.user_id, res.display_name);
 			goto('/admin');
 		} catch (e) {
 			if (e instanceof ApiError) {