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>

src/database/schema.rs

@@ -216,6 +216,13 @@ diesel::table! {
         backend -> Text,
         fewshot_source_ids -> Nullable<Text>,
         content_hash -> Nullable<Text>,
+        num_ctx -> Nullable<Integer>,
+        temperature -> Nullable<Float>,
+        top_p -> Nullable<Float>,
+        top_k -> Nullable<Integer>,
+        min_p -> Nullable<Float>,
+        system_prompt -> Nullable<Text>,
+        persona_id -> Nullable<Text>,
     }
 }