feat(ai): few-shot exemplars + sticky Ollama preference

- Few-shot injection on /insights/generate/agentic: compresses prior
  training_messages into trajectory blocks (tool calls + result summaries)
  and injects into the system prompt. Hardcoded default ids with optional
  request override.
- New fewshot_source_ids column on photo_insights (+ migration) to track
  which exemplars influenced a given row, for downstream training-set
  filtering. Chat amend rows stamp None with a lineage note.
- Ollama client now remembers which server (primary/fallback) most
  recently succeeded and tries it first on the next call, via a shared
  Arc<AtomicBool>. Avoids re-404ing the primary on every agent iteration
  when the chosen model only lives on the fallback.
- Demote noisy logs: daily_summary "Summary match" lines to debug;
  inner chat_with_tools non-2xx body log from error to warn (outer
  layer owns the terminal-error signal).
- Drift-guard tests for summarize_tool_result covering the success /
  empty / error / unknown shape for every tool.
- Tidy: three pre-existing clippy warnings cleaned up.

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

src/ai/insight_chat.rs

@@ -502,6 +502,11 @@ impl InsightChatService {
                 .await?;
             let title = title_raw.trim().trim_matches('"').to_string();
 
+            // Amended rows intentionally do not inherit the parent's
+            // `fewshot_source_ids`. The parent's few-shot influence is still
+            // present in this row's content; if you want strict lineage
+            // tracking for training-set filtering, fetch the parent here and
+            // copy its value forward.
             let new_row = InsertPhotoInsight {
                 library_id: req.library_id,
                 file_path: normalized.clone(),
@@ -512,6 +517,7 @@ impl InsightChatService {
                 is_current: true,
                 training_messages: Some(json),
                 backend: effective_backend.clone(),
+                fewshot_source_ids: None,
             };
             let cx = opentelemetry::Context::new();
             let mut dao = self.insight_dao.lock().expect("Unable to lock InsightDao");
@@ -608,7 +614,7 @@ impl InsightChatService {
     ) -> BoxStream<'static, ChatStreamEvent> {
         let svc = self;
         let s = async_stream::stream! {
-            match svc.chat_turn_stream_inner(req, |ev| Ok(ev)).await {
+            match svc.chat_turn_stream_inner(req, Ok).await {
                 Ok(mut rx) => {
                     while let Some(ev) = rx.recv().await {
                         yield ev;
@@ -955,6 +961,11 @@ impl InsightChatService {
                 .await?;
             let title = title_raw.trim().trim_matches('"').to_string();
 
+            // Amended rows intentionally do not inherit the parent's
+            // `fewshot_source_ids`. The parent's few-shot influence is still
+            // present in this row's content; if you want strict lineage
+            // tracking for training-set filtering, fetch the parent here and
+            // copy its value forward.
             let new_row = InsertPhotoInsight {
                 library_id: req.library_id,
                 file_path: normalized.clone(),
@@ -965,6 +976,7 @@ impl InsightChatService {
                 is_current: true,
                 training_messages: Some(json),
                 backend: effective_backend.clone(),
+                fewshot_source_ids: None,
             };
             let cx = opentelemetry::Context::new();
             let mut dao = self.insight_dao.lock().expect("Unable to lock InsightDao");