fix(render): export INSERT used wrong column + lowercase enum labels (the real 500)

The output-upload-url 500 was NOT the enum cast — it was:
1. INSERT referenced original_project_id; the exports table column is project_id
2. file_type/create_type literals were lowercase ('video'/'render') but the
   export_file_type/export_create_type enums are PascalCase ('Video'/'Render')

Verified the corrected INSERT against the live schema. Now real renders produce
a downloadable export instead of completing with export=nil.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/render/internal/db/db.go

@@ -656,14 +656,14 @@ func (s *Store) CreateExportForJob(ctx context.Context, jobID uuid.UUID) (*model
 
 	_, err = s.pool.Exec(ctx, `
 		INSERT INTO render.exports
-			(id, tenant_id, user_id, saved_project_id, original_project_id,
+			(id, tenant_id, user_id, saved_project_id, project_id,
 			 render_job_id, path, file_extension, file_type, render_quality,
 			 create_type, size_bytes, produce_date, auto_delete_date,
 			 delete_notified, created_at)
 		VALUES
 			($1, $2, $3, $4, $5,
-			 $6, $7, 'mp4', 'video'::render.export_file_type, $8::render.render_quality,
-			 'render'::render.export_create_type, 0, $9, $10,
+			 $6, $7, 'mp4', 'Video'::render.export_file_type, $8::render.render_quality,
+			 'Render'::render.export_create_type, 0, $9, $10,
 			 false, $9)`,
 		exportID, job.TenantID, job.UserID, job.SavedProjectID, job.OriginalProjectID,
 		job.ID, path, job.Quality,