Phase 39: Provider Adapter Refactor

- ProviderAdapter trait with chat(), embed(), unload(), health()
- OllamaAdapter wrapping existing AiClient
- OpenRouterAdapter for openrouter.ai API integration
- provider_key() routing by model prefix (openrouter/*, etc)

crates/aibridge/src/provider.rs

@@ -0,0 +1,39 @@
+use async_trait::async_trait;
+use crate::client::{GenerateRequest, GenerateResponse, EmbedRequest, EmbedResponse};
+
+#[async_trait]
+pub trait ProviderAdapter: Send + Sync {
+    /// Name for routing (ollama, openrouter, etc.)
+    fn name(&self) -> &str;
+
+    /// Chat completion — returns text, model, token counts
+    async fn chat(&self, req: GenerateRequest) -> Result<GenerateResponse, String>;
+
+    /// Embeddings — returns vectors, model, dimensions
+    async fn embed(&self, req: EmbedRequest) -> Result<EmbedResponse, String>;
+
+    /// Unload model from VRAM (optional, no-op if not supported)
+    async fn unload(&self, _model: &str) -> Result<(), String> {
+        Ok(())
+    }
+
+    /// Health check
+    async fn health(&self) -> Result<serde_json::Value, String>;
+}
+
+/// Routing key extracted from model name.
+/// - "qwen3.5:latest" → "ollama"
+/// - "openrouter/anthropic/claude-3.5-sonnet" → "openrouter"
+/// - "gpt-4o" → "ollama" (default)
+pub fn provider_key(model: &str) -> &'static str {
+    let lower = model.to_lowercase();
+    if lower.starts_with("openrouter/") {
+        "openrouter"
+    } else if lower.starts_with("gemini") {
+        "gemini"
+    } else if lower.starts_with("claude") {
+        "claude"
+    } else {
+        "ollama"  // default: local Ollama
+    }
+}