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/translator/response/openai-to-antigravity.js

@@ -1,5 +1,6 @@
 import { register } from "../index.js";
 import { FORMATS } from "../formats.js";
+import { GEMINI_ROLE, OPENAI_FINISH, GEMINI_FINISH } from "../schema/index.js";
 
 // Convert OpenAI SSE chunk to Antigravity SSE format
 // Real Antigravity format:
@@ -79,17 +80,17 @@ export function openaiToAntigravityResponse(chunk, state) {
   }
 
   // Build candidate
-  const candidate = { content: { role: "model", parts } };
+  const candidate = { content: { role: GEMINI_ROLE.MODEL, parts } };
 
   // Finish reason mapping
   if (finishReason) {
     const reasonMap = {
-      "stop": "STOP",
-      "length": "MAX_TOKENS",
-      "tool_calls": "STOP",
-      "content_filter": "SAFETY"
+      [OPENAI_FINISH.STOP]: GEMINI_FINISH.STOP,
+      [OPENAI_FINISH.LENGTH]: GEMINI_FINISH.MAX_TOKENS,
+      [OPENAI_FINISH.TOOL_CALLS]: GEMINI_FINISH.STOP,
+      [OPENAI_FINISH.CONTENT_FILTER]: GEMINI_FINISH.SAFETY
     };
-    candidate.finishReason = reasonMap[finishReason] || "STOP";
+    candidate.finishReason = reasonMap[finishReason] || GEMINI_FINISH.STOP;
   }
 
   // Build response