Replace Anthropic provider todo!() stubs with typed errors; panics abort in release

src-tauri/src/llm/mod.rs

@@ -542,10 +542,19 @@ pub struct AnthropicProvider {
 #[async_trait]
 impl LlmProvider for AnthropicProvider {
     async fn status(&self) -> LlmStatus {
-        todo!("Phase 10a — Anthropic status")
+        // Not built yet (Phase 10a) and not reachable today: `set_llm_provider`
+        // rejects "anthropic" before settings could ever select this provider.
+        LlmStatus {
+            provider: "anthropic".to_string(),
+            reachable: false,
+            is_local: false,
+            models: Vec::new(),
+        }
     }
     async fn summarize(&self, _prompt: Prompt, _out: TokenSink) -> Result<Summary, LlmError> {
-        todo!("Phase 10a — POST /v1/messages streaming")
+        Err(LlmError::Request(
+            "Anthropic provider isn't built yet (Phase 10a)".to_string(),
+        ))
     }
     fn is_local(&self) -> bool {
         false