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/database/insights_dao.rs

@@ -38,6 +38,16 @@ pub trait InsightDao: Sync + Send {
         file_path: &str,
     ) -> Result<Vec<PhotoInsight>, DbError>;
 
+    /// Fetch a single insight by primary key, regardless of `is_current`.
+    /// Used by the few-shot injection flow where the caller picks specific
+    /// historical insights (which may have been superseded) as training
+    /// exemplars for a fresh generation.
+    fn get_insight_by_id(
+        &mut self,
+        context: &opentelemetry::Context,
+        insight_id: i32,
+    ) -> Result<Option<PhotoInsight>, DbError>;
+
     fn delete_insight(
         &mut self,
         context: &opentelemetry::Context,
@@ -198,6 +208,25 @@ impl InsightDao for SqliteInsightDao {
         .map_err(|_| DbError::new(DbErrorKind::QueryError))
     }
 
+    fn get_insight_by_id(
+        &mut self,
+        context: &opentelemetry::Context,
+        insight_id: i32,
+    ) -> Result<Option<PhotoInsight>, DbError> {
+        trace_db_call(context, "query", "get_insight_by_id", |_span| {
+            use schema::photo_insights::dsl::*;
+
+            let mut connection = self.connection.lock().expect("Unable to get InsightDao");
+
+            photo_insights
+                .find(insight_id)
+                .first::<PhotoInsight>(connection.deref_mut())
+                .optional()
+                .map_err(|_| anyhow::anyhow!("Query error"))
+        })
+        .map_err(|_| DbError::new(DbErrorKind::QueryError))
+    }
+
     fn delete_insight(
         &mut self,
         context: &opentelemetry::Context,