feat: async insight generation with SQLite job tracking

- Add insight_generation_jobs table migration and DAO
- Implement job lifecycle: create_or_get_active, complete, fail, cancel
- Refactor POST /insights/generate and /agentic to async spawn with timeout
- Add GET /insights/generation/status endpoint with job_id and file_path lookup
- Use String for enum fields in Diesel models to avoid private Bound type
- Add from_str() helpers on InsightJobStatus and InsightGenerationType
- Fix update_training_messages to return Result<usize, DbError>
- 7/7 DAO unit tests passing

src/ai/insight_generator.rs

@@ -196,6 +196,12 @@ impl InsightGenerator {
         }
     }
 
+    /// Accessor for the insight DAO (used by async job completion to
+    /// look up the stored insight id).
+    pub fn insight_dao(&self) -> &Arc<Mutex<Box<dyn InsightDao>>> {
+        &self.insight_dao
+    }
+
     /// Whether the optional Apollo Places integration is wired up. Drives
     /// tool-definition gating (no point offering `get_personal_place_at`
     /// when Apollo is unreachable) — exposed publicly so `insight_chat`