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/database/mod.rs

@@ -45,6 +45,7 @@ pub struct DuplicateRow {
 
 pub mod calendar_dao;
 pub mod daily_summary_dao;
+pub mod insight_generation_job_dao;
 pub mod insights_dao;
 pub mod knowledge_dao;
 pub mod location_dao;
@@ -57,6 +58,7 @@ pub mod search_dao;
 
 pub use calendar_dao::{CalendarEventDao, SqliteCalendarEventDao};
 pub use daily_summary_dao::{DailySummaryDao, InsertDailySummary, SqliteDailySummaryDao};
+pub use insight_generation_job_dao::{InsightGenerationJobDao, SqliteInsightGenerationJobDao};
 pub use insights_dao::{InsightDao, SqliteInsightDao};
 pub use knowledge_dao::{
     ConsolidationGroup, EntityFilter, EntityGraph, EntityPatch, EntitySort, FactFilter, FactPatch,