feat(ai): hybrid backend mode for agentic insights

Adds a `backend` column to photo_insights (default 'local', migration
2026-04-20-000000) and a corresponding optional `backend` field on the
agentic request. When a request sets backend=hybrid:

- The local Ollama vision model is called once via describe_image to
  produce a text description.
- The description is inlined into the first user message as text —
  no base64 image is ever sent to the chat model.
- The agentic tool-calling loop and title generation route through an
  OpenRouterClient (dispatched via &dyn LlmClient), letting the user
  pick any tool-capable model from OpenRouter per request.
- describe_photo is removed from the offered tools since the description
  is already present.

Embeddings and vision stay on local Ollama regardless of backend.
Hybrid mode requires OPENROUTER_API_KEY; handlers return a clear error
when hybrid is requested without it, and also when the selected
OpenRouter model lacks tool-calling support.

AppState gains an optional openrouter client built from
OPENROUTER_API_KEY / OPENROUTER_BASE_URL / OPENROUTER_DEFAULT_MODEL /
OPENROUTER_EMBEDDING_MODEL / attribution headers. Default model is
anthropic/claude-sonnet-4.

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

src/state.rs

@@ -1,3 +1,4 @@
+use crate::ai::openrouter::OpenRouterClient;
 use crate::ai::{InsightGenerator, OllamaClient, SmsApiClient};
 use crate::database::{
     CalendarEventDao, DailySummaryDao, ExifDao, InsightDao, KnowledgeDao, LocationHistoryDao,
@@ -31,6 +32,13 @@ pub struct AppState {
     pub preview_clips_path: String,
     pub excluded_dirs: Vec<String>,
     pub ollama: OllamaClient,
+    /// `None` when `OPENROUTER_API_KEY` is not configured. Consulted only
+    /// when a request explicitly opts into `backend=hybrid`. Currently
+    /// reached via `insight_generator`; kept here so future handlers
+    /// (insight_chat) can route to it without threading it through the
+    /// generator.
+    #[allow(dead_code)]
+    pub openrouter: Option<Arc<OpenRouterClient>>,
     pub sms_client: SmsApiClient,
     pub insight_generator: InsightGenerator,
 }
@@ -61,6 +69,7 @@ impl AppState {
         preview_clips_path: String,
         excluded_dirs: Vec<String>,
         ollama: OllamaClient,
+        openrouter: Option<Arc<OpenRouterClient>>,
         sms_client: SmsApiClient,
         insight_generator: InsightGenerator,
         preview_dao: Arc<Mutex<Box<dyn PreviewDao>>>,
@@ -92,6 +101,7 @@ impl AppState {
             preview_clips_path,
             excluded_dirs,
             ollama,
+            openrouter,
             sms_client,
             insight_generator,
         }
@@ -127,6 +137,8 @@ impl Default for AppState {
             ollama_fallback_model,
         );
 
+        let openrouter = build_openrouter_from_env();
+
         let sms_api_url =
             env::var("SMS_API_URL").unwrap_or_else(|_| "http://localhost:8000".to_string());
         let sms_api_token = env::var("SMS_API_TOKEN").ok();
@@ -168,6 +180,7 @@ impl Default for AppState {
         // Initialize InsightGenerator with all data sources
         let insight_generator = InsightGenerator::new(
             ollama.clone(),
+            openrouter.clone(),
             sms_client.clone(),
             insight_dao.clone(),
             exif_dao.clone(),
@@ -195,6 +208,7 @@ impl Default for AppState {
             preview_clips_path,
             Self::parse_excluded_dirs(),
             ollama,
+            openrouter,
             sms_client,
             insight_generator,
             preview_dao,
@@ -202,6 +216,25 @@ impl Default for AppState {
     }
 }
 
+/// Build an `OpenRouterClient` from environment variables. Returns `None`
+/// when `OPENROUTER_API_KEY` is unset (the hybrid backend is then
+/// unavailable and requests for it return a clear error).
+fn build_openrouter_from_env() -> Option<Arc<OpenRouterClient>> {
+    let api_key = env::var("OPENROUTER_API_KEY").ok()?;
+    let base_url = env::var("OPENROUTER_BASE_URL").ok();
+    let default_model = env::var("OPENROUTER_DEFAULT_MODEL")
+        .unwrap_or_else(|_| "anthropic/claude-sonnet-4".to_string());
+    let mut client = OpenRouterClient::new(api_key, base_url, default_model);
+    client.set_attribution(
+        env::var("OPENROUTER_HTTP_REFERER").ok(),
+        env::var("OPENROUTER_APP_TITLE").ok(),
+    );
+    if let Ok(model) = env::var("OPENROUTER_EMBEDDING_MODEL") {
+        client.set_embedding_model(model);
+    }
+    Some(Arc::new(client))
+}
+
 #[cfg(test)]
 impl AppState {
     /// Creates an AppState instance for testing with temporary directories
@@ -255,6 +288,7 @@ impl AppState {
         };
         let insight_generator = InsightGenerator::new(
             ollama.clone(),
+            None,
             sms_client.clone(),
             insight_dao.clone(),
             exif_dao.clone(),
@@ -286,6 +320,7 @@ impl AppState {
             preview_clips_path.to_string_lossy().to_string(),
             Vec::new(), // No excluded directories for test state
             ollama,
+            None,
             sms_client,
             insight_generator,
             preview_dao,