feat(qoder): port Kiro-style provider integration with COSY signing

Replaces the Qoder placeholder with a real free-tier provider:

- Device-flow OAuth: PKCE + nonce generated locally, user authorizes at
  qoder.com/device/selectAccounts, poll openapi.qoder.sh until token
- COSY signing (RSA-1024 + AES-128-CBC + MD5) for chat / model-list
- WAF-bypass body encoding (custom-alphabet base64 + thirds rearrange)
- Live model_config catalog from /algo/api/v2/model/list, cached 1h
- 11 models registered (auto/ultimate/performance/efficient/lite +
  6 frontier *model ids)
- Usage fetcher for openapi.qoder.sh/api/v2/quota/usage
- Dashboard live-models resolver, provider test, OAuth modal hookup
- 24 unit tests covering encoder, PKCE, COSY headers, sigPath stripping

open-sse/services/model.js

@@ -14,6 +14,8 @@ const ALIAS_TO_PROVIDER_ID = {
   cl: "cline",
   oc: "opencode",
   ocg: "opencode-go",
+  qd: "qoder",
+  qoder: "qoder",
   // TTS providers
   el: "elevenlabs",
   // API Key providers