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/schema/index.js

@@ -0,0 +1,8 @@
+// Translator schema barrel — pure data enums (roles, blocks). No logic here.
+export { ROLE, GEMINI_ROLE } from "./roles.js";
+export {
+  OPENAI_BLOCK, CLAUDE_BLOCK, RESPONSES_ITEM,
+  VALID_OPENAI_CONTENT_TYPES, VALID_OPENAI_MESSAGE_TYPES,
+} from "./blocks.js";
+export { OPENAI_FINISH, CLAUDE_STOP, GEMINI_FINISH } from "./finishReasons.js";
+export { MODEL_FALLBACK, DEFAULT_IMAGE_MIME } from "./defaults.js";