feat: add manual SD card data upload for offline NRLs; rename RecordingSession to MonitoringSession

- Add POST /api/projects/{project_id}/nrl/{location_id}/upload-data endpoint
  accepting a ZIP or multi-file select of .rnd/.rnh files from an SD card.
  Parses .rnh metadata for session start/stop times, serial number, and store
  name. Creates a MonitoringSession (no unit assignment required) and DataFile
  records for each measurement file.

- Add Upload Data button and collapsible upload panel to the NRL detail Data
  Files tab, with inline success/error feedback and automatic file list refresh
  via HTMX after import.

- Rename RecordingSession -> MonitoringSession throughout the codebase
  (models.py, projects.py, project_locations.py, scheduler.py, roster_rename.py,
  main.py, init_projects_db.py, scripts/rename_unit.py). DB table renamed from
  recording_sessions to monitoring_sessions; old indexes dropped and recreated.

- Update all template UI copy from Recording Sessions to Monitoring Sessions
  (nrl_detail, projects/detail, session_list, schedule_oneoff, roster).

- Add backend/migrate_rename_recording_to_monitoring_sessions.py for applying
  the table rename on production databases before deploying this build.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

templates/partials/projects/file_list.html

@@ -151,9 +151,9 @@
         <svg class="w-16 h-16 mx-auto mb-4 text-gray-400" fill="none" stroke="currentColor" viewBox="0 0 24 24">
             <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M7 21h10a2 2 0 002-2V9.414a1 1 0 00-.293-.707l-5.414-5.414A1 1 0 0012.586 3H7a2 2 0 00-2 2v14a2 2 0 002 2z"></path>
         </svg>
-        <p class="text-gray-500 dark:text-gray-400 mb-2">No files downloaded yet</p>
+        <p class="text-gray-500 dark:text-gray-400 mb-2">No data files yet</p>
         <p class="text-sm text-gray-400 dark:text-gray-500">
-            Files will appear here once they are downloaded from the sound level meter
+            Files appear here after an FTP download from a connected meter, or after uploading SD card data manually.
         </p>
     </div>
 {% endif %}