security: medium-severity fixes (proxies, ssrf, uploads, lnurl, github_data)

- Trust the Forge reverse proxy and force https URLs in production so
  generated absolute URLs match the actual TLS termination.
- Reject Nostr profile photo URLs that aren't http(s) or that resolve to
  loopback / private (RFC1918) addresses to close an SSRF vector in
  FetchNostrProfileJob.
- Tighten image upload validation across meetup, course, and lecturer
  create/edit components: explicit mimes whitelist (jpeg, png, webp),
  max 5 MiB, and dimension cap of 4000x4000.
- Replace the silent "skip if exists" branch in LnurlAuthController with
  updateOrCreate so concurrent callers cannot race on the k1 record.
- Validate github_data on Meetup edit, decoding the JSON, and keep only
  the whitelisted keys (top, left, state) with strict type coercion to
  prevent storing arbitrary attacker-controlled JSON.

bootstrap/app.php

@@ -16,6 +16,8 @@ return Application::configure(basePath: dirname(__DIR__))
         health: '/up',
     )
     ->withMiddleware(function (Middleware $middleware) {
+        $middleware->trustProxies(at: '*');
+
         $middleware->web(append: [
             DomainMiddleware::class,
             LangCountrySession::class,