refactor(open-sse): translator DRY + schema enums, bug fixes, dead code cleanup

- Bug B1-B7: media UI m.kind||m.type, serviceKinds, gemini mediaPriority, schema kind, models/info lookup by kind
- Dead code D1-D6: safeParseJSON, drop PROVIDER_ENDPOINTS, orphan fetcher, GITHUB_CONFIG derive, getProviderConfig internal, legacy kiro file
- Translator concerns: toOpenAIUsage, toOpenAIFinish (gemini/kiro/ollama + fix kiro tool finish), thinking effort maps
- Reorg helpers/ → concerns/ (logic) + formats/ (per-format) + schema/ (pure enums: roles/blocks/finishReasons/defaults)
- Wire ~280 hardcoded role/block/finish/default literals to schema enums across 20+ files
- collapseTextParts + extractTextContent dedup
- Normalize translator fn names to openaiToXRequest / xToOpenAIResponse
- Golden tests lock behavior; 0 regression (byte-for-byte providers/alias, 26=26 known fails)

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

open-sse/executors/cursor.js

@@ -142,7 +142,7 @@ export class CursorExecutor extends BaseExecutor {
 
   transformRequest(model, body, stream, credentials) {
     // Messages are already translated by chatCore (claude→openai→cursor)
-    // Do NOT call buildCursorRequest again — double-translation drops tool_results
+    // Do NOT call openaiToCursorRequest again — double-translation drops tool_results
     const messages = body.messages || [];
     const tools = body.tools || [];
     const reasoningEffort = body.reasoning_effort || null;