refactor(open-sse): B1 consolidate media endpoint URLs into registry

- image/embed/tts/search base URLs derive from media.*Config.baseUrl /
  searchViaChat.endpoint (single source); handlers read PROVIDER_MEDIA.
- ~18 hardcoded endpoints moved: bfl/fal/stability/runway/hf/gemini/
  cloudflare/recraft/sdwebui/comfyui/nanobanana image, voyage embed,
  gemini/openrouter tts, chatSearch endpoints.
- Byte-identical: PROVIDERS 62 + alias 90 baselines, image buildUrl outputs.

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

open-sse/handlers/imageProviders/stabilityAi.js

@@ -1,7 +1,8 @@
 // Stability AI v2 — sync, returns { image: "<b64>" }
 import { nowSec, sizeToAspectRatio } from "./_base.js";
+import { PROVIDER_MEDIA } from "../../providers/index.js";
 
-const BASE_URL = "https://api.stability.ai/v2beta/stable-image/generate";
+const BASE_URL = PROVIDER_MEDIA["stability-ai"]?.imageConfig?.baseUrl;
 
 // Map model id → endpoint segment
 function modelToEndpoint(model) {