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/join/+page.svelte

@@ -1,9 +1,21 @@
 <script lang="ts">
+	import { onMount } from 'svelte';
 	import { goto } from '$app/navigation';
 	import { api, ApiError } from '$lib/api';
 	import { setAuth } from '$lib/auth';
 	import { focusTrap } from '$lib/actions/focus-trap';
 
+	// Show which event the guest is joining (USER_JOURNEYS §1). Public, pre-auth.
+	let eventName = $state('');
+	onMount(async () => {
+		try {
+			const ev = await api.get<{ name: string; slug: string }>('/event');
+			eventName = ev.name;
+		} catch {
+			// Non-fatal — fall back to the generic heading if the lookup fails.
+		}
+	});
+
 	let displayName = $state('');
 	let error = $state('');
 	let loading = $state(false);
@@ -164,6 +176,9 @@
 		{:else}
 			<!-- Normal join form -->
 			<h1 class="mb-2 text-center text-2xl font-bold text-gray-900 dark:text-gray-100">Willkommen!</h1>
+			{#if eventName}
+				<p class="mb-1 text-center text-lg font-semibold text-blue-600 dark:text-blue-400" data-testid="join-event-name">{eventName}</p>
+			{/if}
 			<p class="mb-6 text-center text-gray-600 dark:text-gray-400">Gib deinen Namen ein, um dem Event beizutreten.</p>
 
 			<form onsubmit={(e) => { e.preventDefault(); handleJoin(); }}>