feat: Anthropic provider/inbound + embeddings

- Anthropic outbound provider: /v1/messages, system extraction, x-api-key +
  anthropic-version; streaming translates Anthropic SSE -> unified OpenAI wire format
- Anthropic inbound adapter (POST /v1/messages): non-streaming JSON + streaming SSE
  (OpenAI -> Anthropic event translation)
- Embeddings: POST /v1/embeddings inbound + Provider::embed(); embedding models
  resolvable from the pool (registry no longer skips them)
- protocols mounted always, gated on live flags; admin meta marks them implemented

src/registry.rs

@@ -15,9 +15,6 @@ impl Registry {
     pub fn from_config(cfg: &Config, secrets: &SecretStore) -> anyhow::Result<Self> {
         let mut by_id: HashMap<String, Arc<dyn Provider>> = HashMap::new();
         for m in &cfg.models {
-            if m.kind == "embedding" {
-                continue; // embedding models are handled by a separate branch (v0.1)
-            }
             // provider key: secret store → environment variable
             let api_key = m
                 .api_key_env