feat(reports): manual run/view endpoints for the night report

Add backend/routers/reports.py (registered in main.py):
- GET  /api/projects/{id}/reports/nightly/view — render the night report
  HTML inline (preview; no write, no email)
- POST /api/projects/{id}/reports/nightly/run  — build -> write
  report.html/report.json to disk -> dry-run email -> JSON result + view_url

Same entry point the scheduled morning tick will reuse. Query params:
night_date (default last night, local tz), baseline_start/end, metrics, send.
Orchestrator now also returns the rendered html for inline display.

Verified via FastAPI TestClient on real meter data (200 HTML with the computed
numbers, files written to disk, 400/404 validation paths).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/services/report_orchestrator.py

@@ -118,6 +118,7 @@ def run_nightly_report(
         "location_count": len(report.locations),
         "html_path": str(html_path),
         "json_path": str(json_path),
+        "html": html,            # for callers that want to display it inline
         "email": email_result,
     }
     logger.info(