Fix security and correctness issues found in full-codebase audit

- Restrict meetingPassword field so it isn't leaked via the public REST/GraphQL API
- Fix booking slot computation to use Europe/Berlin time instead of the server's UTC clock
- Reset email verification when a customer changes their email address
- Fix ICS calendar injection via unescaped carriage returns in event descriptions
- Bind WebRTC meeting kicks to a persistent client id so they survive a rejoin
- Move the meeting signaling token out of the WebSocket query string into the first message
- Prevent duplicate signaling connections from leaking when the same participant reconnects
- Use the rightmost X-Forwarded-For entry for rate limiting (single trusted reverse proxy)
- Use constant-time comparison for the cron endpoint's bearer token
- Remove SVG from allowed Media upload types (stored-XSS risk, unused anyway)
- Add baseline security headers and a CSP to next.config.ts
- Fix CI/CD script injection via unsanitized git ref names in release.yml

app/(payload)/api/meetings/[slug]/join/route.ts

@@ -20,7 +20,7 @@ type Args = { params: Promise<{ slug: string }> };
 export async function POST(request: Request, { params }: Args) {
   const { slug } = await params;
 
-  let body: { name?: unknown; password?: unknown };
+  let body: { name?: unknown; password?: unknown; clientId?: unknown };
   try {
     body = await request.json();
   } catch {
@@ -29,6 +29,7 @@ export async function POST(request: Request, { params }: Args) {
 
   const name = typeof body.name === "string" ? body.name.trim() : "";
   const password = typeof body.password === "string" ? body.password.trim() : "";
+  const clientId = typeof body.clientId === "string" ? body.clientId.trim() : undefined;
   if (!name) {
     return NextResponse.json({ error: "Bitte gib deinen Namen ein." }, { status: 400 });
   }
@@ -85,6 +86,10 @@ export async function POST(request: Request, { params }: Args) {
       eventSlug: slug,
       name,
       role: isHost ? "host" : "participant",
+      // Only meaningful for participants — a host authenticates via a real
+      // session already, so there's no need to anchor a kick to it (and
+      // hosts can't be kicked in the first place, see signalingServer.ts).
+      clientId: isHost ? undefined : clientId,
     });
 
     return NextResponse.json({