feat: monitoring session improvements — UTC fix, period hours, calendar, session detail

- Fix UTC display bug: upload_nrl_data now wraps RNH datetimes with
  local_to_utc() before storing, matching patch_session behavior.
  Period type and label are derived from local time before conversion.

- Add period_start_hour / period_end_hour to MonitoringSession model
  (nullable integers 0–23). Migration: migrate_add_session_period_hours.py

- Update patch_session to accept and store period_start_hour / period_end_hour.
  Response now includes both fields.

- Update get_project_sessions to compute "Effective: M/D H:MM AM → M/D H:MM AM"
  string from period hours and pass it to session_list.html.

- Rework period edit UI in session_list.html: clicking the period badge now
  opens an inline editor with period type selector + start/end hour inputs.
  Selecting a period type pre-fills default hours (Day: 7–19, Night: 19–7).

- Wire period hours into _build_location_data_from_sessions: uses
  period_start/end_hour when set, falls back to hardcoded defaults.

- RND viewer: inject SESSION_PERIOD_START/END_HOUR from template context.
  renderTable() dims rows outside the period window (opacity-40) with a
  tooltip; shows "(N in period window)" in the row count.

- New session detail page at /api/projects/{id}/sessions/{id}/detail:
  shows breadcrumb, files list with View/Download/Report actions,
  editable session info form (label, period type, hours, times).

- Add local_datetime_input Jinja filter for datetime-local input values.

- Monthly calendar view: new get_sessions_calendar endpoint returns
  sessions_calendar.html partial; added below sessions list in detail.html.
  Color-coded per NRL with legend, HTMX prev/next navigation, session dots
  link to detail page.

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

backend/routers/project_locations.py

@@ -31,6 +31,7 @@ from backend.models import (
     DataFile,
 )
 from backend.templates_config import templates
+from backend.utils.timezone import local_to_utc
 
 router = APIRouter(prefix="/api/projects/{project_id}", tags=["project-locations"])
 
@@ -824,8 +825,15 @@ async def upload_nrl_data(
             rnh_meta = _parse_rnh(fbytes)
             break
 
-    started_at = _parse_rnh_datetime(rnh_meta.get("start_time_str")) or datetime.utcnow()
-    stopped_at = _parse_rnh_datetime(rnh_meta.get("stop_time_str"))
+    # RNH files store local time (no UTC offset).  Use local values for period
+    # classification / label generation, then convert to UTC for DB storage so
+    # the local_datetime Jinja filter displays the correct time.
+    started_at_local = _parse_rnh_datetime(rnh_meta.get("start_time_str")) or datetime.utcnow()
+    stopped_at_local = _parse_rnh_datetime(rnh_meta.get("stop_time_str"))
+
+    started_at = local_to_utc(started_at_local)
+    stopped_at = local_to_utc(stopped_at_local) if stopped_at_local else None
+
     duration_seconds = None
     if started_at and stopped_at:
         duration_seconds = int((stopped_at - started_at).total_seconds())
@@ -835,8 +843,9 @@ async def upload_nrl_data(
     index_number = rnh_meta.get("index_number", "")
 
     # --- Step 3: Create MonitoringSession ---
-    period_type = _derive_period_type(started_at) if started_at else None
-    session_label = _build_session_label(started_at, location.name, period_type) if started_at else None
+    # Use local times for period/label so classification reflects the clock at the site.
+    period_type = _derive_period_type(started_at_local) if started_at_local else None
+    session_label = _build_session_label(started_at_local, location.name, period_type) if started_at_local else None
 
     session_id = str(uuid.uuid4())
     monitoring_session = MonitoringSession(