security: v2.0 — AES-GCM crypto, SSRF guards, rate limits, hardening

Breaking wire-format change: dual-read (V1+V2) / single-write (V2) so
existing user secrets, stored messages, and inter-tenant key keep
working. Old clients and relays lose cross-version chat until both
sides are upgraded.

Relay
- Switch clientEncrypt/masterEncrypt to AES-256-GCM with HKDF-derived
  per-ciphertext salts; keep CBC-V1 fallback on decrypt only.
- On-bootstrap migration re-envelopes tenant secret_encrypted and the
  inter-tenant key to GCM-V2 (idempotent).
- CORS: stop reflecting arbitrary Origin; allow own origin + optional
  RELAY_CORS_ORIGINS env allowlist; drop Access-Control-Allow-Credentials.
- Generic error messages replace "no such user: <name>" enumeration.
- Exception messages no longer echoed back; logged server-side.
- Collab-lock max hold capped at 10min so a member can't grief-refresh
  forever.
- Attachment filenames validated against hex.<ext> pattern.
- Passwords min length 10; /api/account/password rate-limited.

App / Electron client
- Shared hyprcrdRelayEncrypt/Decrypt helpers (GCM-V2 write, V1 read).
- Chat + collab-buckets plugins delegate to the shared helpers.
- Poll + push + attachments migrated to the dual-format path.
- /api/relay/settings GET returns has_key boolean; secret never echoed.
- Setup endpoint now CSRF-checked.
- SSRF: CURLOPT_PROTOCOLS restricted to HTTP(S) everywhere; bookmarks
  favicon fetch also blocks private/loopback/link-local.
- Login / password-change rate limiter moved to DB-backed IP keying.
- Passwords min length 10 throughout.
- Zip import enforces per-file (25MB) and total (500MB) caps, extension
  allowlist, no-overwrite.
- Verbose relay-push debug gated behind APP_DEBUG env.

Version bumped to 2.0.0 (protocol-breaking).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

relay/inc/routes/account.php

@@ -52,11 +52,14 @@ if ($route === '/api/account/secret' && $method === 'DELETE') {
 
 if ($route === '/api/account/password' && $method === 'POST') {
     if (!$sessionTenant) jsonResponse(['error' => 'not logged in'], 401);
+    // Rate-limit password changes — a stolen session cookie could otherwise
+    // brute-force the `current` field server-side with no friction.
+    if (isRateLimited($db, 'account-password', 10)) jsonResponse(['error' => 'too many attempts'], 429);
     $input = json_decode(file_get_contents('php://input'), true) ?: [];
     $current = (string)($input['current'] ?? '');
     $new = (string)($input['new'] ?? '');
 
-    if (strlen($new) < 4) jsonResponse(['error' => 'new password must be at least 4 chars'], 400);
+    if (strlen($new) < 10) jsonResponse(['error' => 'new password must be at least 10 chars'], 400);
     if (!password_verify($current, $sessionTenant['password_hash'])) {
         jsonResponse(['error' => 'current password is wrong'], 401);
     }