feat(providers/codex): bulk add accounts via JSON

Add a "Bulk Add" button on /dashboard/providers/codex that imports
multiple OAuth accounts at once by pasting a JSON array, single object,
or { accounts: [...] } wrapper.

- New endpoint POST /api/oauth/codex/bulk-import (serial loop, no token echo)
- New BulkImportCodexModal component with JSON textarea + success/failure summary
- Persist idToken/lastRefreshAt on first insert via OPTIONAL_FIELDS
- Backfill email/chatgptAccountId/chatgptPlanType from JWT when missing
- Derive expiresAt from expiresIn when missing
- Gated to providerId === "codex" only; other providers unaffected

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

src/lib/db/repos/connectionsRepo.js

@@ -7,7 +7,7 @@ const OPTIONAL_FIELDS = [
   "accessToken", "refreshToken", "expiresAt", "tokenType",
   "scope", "projectId", "apiKey", "testStatus",
   "lastTested", "lastError", "lastErrorAt", "rateLimitedUntil", "expiresIn", "errorCode",
-  "consecutiveUseCount",
+  "consecutiveUseCount", "idToken", "lastRefreshAt",
 ];
 
 function rowToConn(row) {