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/models.rs

@@ -102,6 +102,12 @@ pub struct InsertPhotoInsight {
     pub training_messages: Option<String>,
     /// `"local"` (Ollama with images) | `"hybrid"` (local vision + OpenRouter chat).
     pub backend: String,
+    /// JSON array of insight ids whose `training_messages` were compressed
+    /// and injected into the system prompt as few-shot exemplars when this
+    /// row was generated. `None` means no few-shot was used (pristine
+    /// generation). Used downstream to filter out contaminated rows when
+    /// assembling an unbiased training / evaluation set.
+    pub fewshot_source_ids: Option<String>,
 }
 
 #[derive(Serialize, Queryable, Clone, Debug)]
@@ -119,6 +125,7 @@ pub struct PhotoInsight {
     pub approved: Option<bool>,
     /// `"local"` (Ollama with images) | `"hybrid"` (local vision + OpenRouter chat).
     pub backend: String,
+    pub fewshot_source_ids: Option<String>,
 }
 
 // --- Libraries ---