feat(providers): self-hosted OpenAI-compatible STT, TTS and embedding providers

Add Self-hosted STT/TTS/Embedding providers that read baseUrl per connection
instead of a fixed registry endpoint, so 9Router can point at whisper.cpp,
faster-whisper, Kokoro-FastAPI, llama-server, vLLM, Infinity, and similar
OpenAI-compatible local servers.

Self-hosted Embedding refuses to run without a baseUrl rather than falling
back to api.openai.com like openaiCompatNode does, since that fallback would
silently send input text and the API key to OpenAI under a provider named
"Self-hosted". Also fixes embeddingsCore to catch adapter build errors as a
400 instead of letting them escape uncaught, and bounds the upstream fetch
with FETCH_CONNECT_TIMEOUT_MS to avoid hanging forever on a dead endpoint.

Self-hosted TTS treats a bare model value as the model rather than the voice,
since the generic OpenAI TTS convention (bare = voice) is backwards for a
provider where the model is the variable part.

open-sse/providers/registry/index.js

@@ -117,6 +117,9 @@ import p113 from "./morph.js";
 // import p104 from "./windsurf.js";
 import p115 from "./poolside.js";
 import p116 from "./tokenrouter.js";
+import p117 from "./selfhosted-stt.js";
+import p118 from "./selfhosted-tts.js";
+import p119 from "./selfhosted-embedding.js";
 
 export default [
   p0,
@@ -235,4 +238,7 @@ export default [
   // p104, // windsurf — hidden, no tool calling
   p115,
   p116,
+  p117,
+  p118,
+  p119,
 ];