feat(offroute): MVUM legal access — pathfinder integration + places panel API + boundary_mode control

MVUM Data Import:
- Downloaded USFS MVUM Roads (150,636 features) and Trails (28,741 features)
- Imported to navi.db as mvum_roads and mvum_trails tables
- Idaho coverage: ~8,994 roads and ~4,504 trails across 7 national forests
- Preserved all vehicle-class fields (ATV, MOTORCYCLE, HIGHCLEARANCEVEHICLE, etc.)
- Preserved seasonal date ranges (*_DATESOPEN fields)

New mvum.py module:
- MVUMReader class for querying MVUM data by bbox and nearest point
- parse_date_range() for seasonal date string parsing (MM/DD-MM/DD format)
- check_access() for determining open/closed status with date checking
- symbol_to_access() fallback when per-vehicle fields are null
- get_mvum_access_grid() for rasterizing MVUM to pathfinder grid

Cost function integration:
- Added mvum parameter to compute_cost_grid()
- MVUM closures respond to boundary_mode:
  * strict = impassable (np.inf)
  * pragmatic = 5x friction penalty
  * emergency = ignored entirely
- Foot mode skips MVUM (motor-vehicle specific)

Router integration:
- Loads MVUM access grid for motorized modes (mtb, atv, vehicle)
- Tracks mvum_closed_crossings in path summary

Places Panel API:
- GET /api/mvum?lat=XX&lon=XX&radius=50
- Returns MVUM feature with access status for all vehicle classes
- Includes seasonal date ranges, maintenance level, forest/district info
- GeoJSON geometry for map display

Validation:
- MVUM places endpoint tested with Sawtooth NF road
- All four modes validated with strict/pragmatic/emergency boundary modes
- Foot mode correctly ignores MVUM restrictions

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/offroute/cost.py

@@ -213,6 +213,7 @@ def compute_cost_grid(
     trails: Optional[np.ndarray] = None,
     barriers: Optional[np.ndarray] = None,
     wilderness: Optional[np.ndarray] = None,
+    mvum: Optional[np.ndarray] = None,
     boundary_mode: Literal["strict", "pragmatic", "emergency"] = "pragmatic",
     mode: Literal["foot", "mtb", "atv", "vehicle"] = "foot"
 ) -> np.ndarray:
@@ -236,6 +237,10 @@ def compute_cost_grid(
                   255 = closed/restricted area (PAD-US Pub_Access = XA).
         wilderness: Optional[np.ndarray] of wilderness values (uint8).
                   255 = designated wilderness area.
+        mvum: Optional[np.ndarray] of MVUM access values (uint8).
+                  0 = no MVUM data, 1 = open, 255 = closed to this mode.
+                  MVUM closures respond to boundary_mode (strict/pragmatic/emergency).
+                  Foot mode should pass None (MVUM is motor-vehicle specific).
         boundary_mode: How to handle barriers ("strict", "pragmatic", "emergency")
         mode: Travel mode ("foot", "mtb", "atv", "vehicle")
 
@@ -392,6 +397,26 @@ def compute_cost_grid(
             cost[barrier_mask] *= PRAGMATIC_BARRIER_MULTIPLIER
             del barrier_mask
 
+    # ─── MVUM closures (motor vehicle restrictions) ──────────────────────────
+    # MVUM only applies to motorized modes, not foot. Foot mode should pass mvum=None.
+    # MVUM closures respond to the same boundary_mode as PAD-US barriers:
+    #   "strict"    = MVUM-closed road/trail is impassable
+    #   "pragmatic" = MVUM-closed road/trail gets 5× friction penalty
+    #   "emergency" = MVUM closures ignored entirely
+    if mvum is not None and mode != "foot" and boundary_mode != "emergency":
+        if mvum.shape != elevation.shape:
+            raise ValueError(f"MVUM shape mismatch")
+
+        # Value 255 = road/trail exists but is closed to this mode
+        mvum_closed_mask = mvum == 255
+
+        if boundary_mode == "strict":
+            np.putmask(cost, mvum_closed_mask, np.inf)
+        elif boundary_mode == "pragmatic":
+            cost[mvum_closed_mask] *= PRAGMATIC_BARRIER_MULTIPLIER
+
+        del mvum_closed_mask
+
     return cost