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/2026-05-27-000000_add_insight_generation_jobs/up.sql

@@ -1,8 +1,7 @@
 -- Track async insight generation jobs so the client can poll for
--- completion after the server returns 202 Accepted. The UNIQUE
--- constraint on (library_id, file_path, generation_type) ensures
--- idempotent inserts: if a running job already exists, the caller
--- should return that job_id instead of creating a duplicate.
+-- completion after the server returns 202 Accepted. Each generation
+-- creates a new row; the application layer cancels prior running
+-- jobs before inserting.
 CREATE TABLE insight_generation_jobs (
     id INTEGER PRIMARY KEY AUTOINCREMENT,
     library_id INTEGER NOT NULL DEFAULT 1,
@@ -12,8 +11,7 @@ CREATE TABLE insight_generation_jobs (
     started_at INTEGER NOT NULL,
     completed_at INTEGER,
     result_insight_id INTEGER,
-    error_message TEXT,
-    UNIQUE(library_id, file_path, generation_type)
+    error_message TEXT
 );
 
 -- For the status endpoint: fast lookup by (library_id, file_path)