fix: audit fixes for async insight jobs + persist generation params

- Fix query param mismatch: rename GenerationStatusQuery.file_path to
  path so the client's app-resume buildQuery({ path: ... }) resolves
  correctly instead of always getting 400
- Remove dead _lib_id bindings from both generate handlers
- Return 202 Accepted instead of 200 from generate endpoints
- Restore OpenTelemetry span instrumentation on generate handlers
- Remove stale UNIQUE constraint from initial migration (incompatible
  with plain-INSERT DAO)
- Add tests for status guard: complete_job/fail_job are no-ops when
  job is already cancelled, and cancel_job by id
- Persist generation params (num_ctx, temperature, top_p, top_k, min_p,
  system_prompt, persona_id) on the photo_insights table for auditing

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

migrations/2026-05-27-000002_add_insight_generation_params/down.sql

@@ -0,0 +1,11 @@
+-- SQLite doesn't support DROP COLUMN before 3.35.0; recreate the table
+-- without the new columns. This is only needed for rollback.
+CREATE TABLE photo_insights_old AS
+    SELECT id, library_id, rel_path, title, summary, generated_at,
+           model_version, is_current, training_messages, approved,
+           backend, fewshot_source_ids, content_hash
+    FROM photo_insights;
+
+DROP TABLE photo_insights;
+
+ALTER TABLE photo_insights_old RENAME TO photo_insights;