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>

tests/translator/AGENTS.md

@@ -14,7 +14,9 @@ Components:
 - `formats.js` — `FORMATS` enum (openai, claude, gemini, gemini-cli, openai-responses, antigravity, kiro, cursor, commandcode, ollama, vertex).
 - `request/<from>-to-<to>.js` — one-way request translation.
 - `response/<from>-to-<to>.js` — one-way SSE response translation.
-- `helpers/` — `openaiHelper.js` (filterToOpenAIFormat), `toolCallHelper.js` (id/arguments), `claudeHelper.js`, `geminiHelper.js`.
+- `schema/` — pure data enums (no logic): `roles.js` (ROLE, GEMINI_ROLE), `blocks.js` (OPENAI_BLOCK, CLAUDE_BLOCK, RESPONSES_ITEM, valid-type lists), `finishReasons.js` (OPENAI_FINISH, CLAUDE_STOP, GEMINI_FINISH), `defaults.js` (MODEL_FALLBACK, DEFAULT_IMAGE_MIME). Import via `schema/index.js`.
+- `concerns/` — cross-format translation LOGIC: `chunk.js`, `usage.js`, `reasoning.js`, `thinking.js` (effort↔budget/level), `toolCall.js`, `finishReason.js` (mapping fns), `image.js`, `json.js`.
+- `formats/` — per-format logic: `openai.js` (filterToOpenAIFormat), `claude.js`, `gemini.js`, `responsesApi.js`, `maxTokens.js`.
 
 **OpenAI-bridge pitfalls** (source of most bugs): going through OpenAI easily loses `thinking`/`reasoning`, image URLs (non-base64), `input_audio`, `is_error`; tool `id`/`index` become unstable (parallel tool calls), non-text system blocks, `tool_choice:"none"`.