fix: prevent hybrid mode from leaking OpenRouter model to local llamacpp client

When backend=hybrid with LLM_BACKEND=llamacpp, the user-selected model
(an OpenRouter id like "google/gemini-3-flash-preview") was being applied
to the local LlamaCppClient's primary_model and vision_model. This caused
describe_image to send the OpenRouter model name to llama-swap, which
returned 400 because it has no such slot.

Guard the local-client model override with !is_hybrid so it only applies
in local-only mode (where the user is selecting a different local model).
Bump to v1.2.0.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ai/backend.rs

@@ -13,7 +13,10 @@ impl BackendKind {
         match s.trim().to_lowercase().as_str() {
             "local" | "" => Ok(Self::Local),
             "hybrid" => Ok(Self::Hybrid),
-            other => Err(anyhow!("unknown backend '{}'; expected 'local' or 'hybrid'", other)),
+            other => Err(anyhow!(
+                "unknown backend '{}'; expected 'local' or 'hybrid'",
+                other
+            )),
         }
     }
 
@@ -65,7 +68,12 @@ impl ResolvedBackend {
         kind: BackendKind,
         images_inline: bool,
     ) -> Self {
-        Self { chat, local, kind, images_inline }
+        Self {
+            chat,
+            local,
+            kind,
+            images_inline,
+        }
     }
 
     pub fn chat(&self) -> &dyn LlmClient {
@@ -97,21 +105,35 @@ mod tests {
 
     #[test]
     fn backend_kind_as_str_roundtrips() {
-        assert_eq!(BackendKind::parse(BackendKind::Local.as_str()).unwrap(), BackendKind::Local);
-        assert_eq!(BackendKind::parse(BackendKind::Hybrid.as_str()).unwrap(), BackendKind::Hybrid);
+        assert_eq!(
+            BackendKind::parse(BackendKind::Local.as_str()).unwrap(),
+            BackendKind::Local
+        );
+        assert_eq!(
+            BackendKind::parse(BackendKind::Hybrid.as_str()).unwrap(),
+            BackendKind::Hybrid
+        );
     }
 
     #[test]
     fn sampling_overrides_has_sampling() {
         let empty = SamplingOverrides {
-            model: None, num_ctx: None, temperature: None,
-            top_p: None, top_k: None, min_p: None,
+            model: None,
+            num_ctx: None,
+            temperature: None,
+            top_p: None,
+            top_k: None,
+            min_p: None,
         };
         assert!(!empty.has_sampling());
 
         let with_temp = SamplingOverrides {
-            model: None, num_ctx: Some(4096), temperature: Some(0.7),
-            top_p: None, top_k: None, min_p: None,
+            model: None,
+            num_ctx: Some(4096),
+            temperature: Some(0.7),
+            top_p: None,
+            top_k: None,
+            min_p: None,
         };
         assert!(with_temp.has_sampling());
     }