fix: prevent non-SSE stream pipe crash and cross-IdP account overwrites (#2244)

- streamingHandler: when upstream returns non-SSE/JSON (e.g. Cloudflare
  5xx HTML), read body, sanitize <title>, notify streamController and
  return a clean JSON error instead of crashing the pipe.
- connectionsRepo: dedup OAuth connections on (email + username) so
  cross-IdP accounts sharing an email no longer overwrite each other;
  workspace providers keep workspace-id matching.
- kimchi: bump User-Agent to 0.1.50, add svg asset + browser-login
  service, and 21 unit tests.

Co-authored-by: Cursor <cursoragent@cursor.com>

open-sse/providers/registry/kimchi.js

@@ -20,7 +20,7 @@ export default {
     baseUrl: "https://llm.kimchi.dev/openai/v1/chat/completions",
     format: "openai",
     headers: {
-      "User-Agent": "kimchi/0.1.40",
+      "User-Agent": "kimchi/0.1.50",
     },
     auth: {
       combined: true,