Add audit log for moderation and admin actions

New audit_log table records actor, action, target and a JSON snapshot
of the details, so entries stay readable after the target is deleted;
the actor is set to NULL when the user is removed. logAudit() is called
from upload delete (single and bulk), comment delete, tag removal, role
create/delete, role permission changes, role assign/revoke and MOTD
updates. Logging failures only warn and never fail the action itself.

The admin page gets an audit card behind the new audit.view permission
with action filter, click-to-filter by user, readable summaries per
action and server-side pagination. Action catalog lives in
shared/utils/audit.ts, labels under admin.auditActions (de/en).

Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/api/admin/motd.put.ts

@@ -6,7 +6,7 @@ const bodySchema = z.object({
 })
 
 export default defineEventHandler(async (event) => {
-  await requirePermission(event, 'site.manage')
+  const actor = await requirePermission(event, 'site.manage')
   const { message } = await readValidatedBody(event, bodySchema.parse)
   const db = useDb()
   await db
@@ -14,5 +14,6 @@ export default defineEventHandler(async (event) => {
     .values({ key: 'motd', value: message })
     .onDuplicateKeyUpdate({ set: { value: message } })
   broadcastToAll({ type: 'motd', message })
+  await logAudit(actor.id, 'update_motd', null, { message })
   return { message }
 })