Add device_type field, mobile-friendly improvements, and device filtering

- Device model: add device_type column (String 50, nullable)
- Device add/edit: type select with presets + custom entry
- Device detail: show type in info card; new Edit Device form
- Device list: Type column + client-side filter bar (type + text search)
- Mobile: card-style responsive tables on dashboard and device list,
  form-grid-2col collapse, larger tap targets, stacked form-actions,
  column picker viewport fix, filter bar full-width controls
- Assign page: larger radio touch targets (min-height 44px)
- 3 new acceptance tests for device_type (45 total)

tests/test_acceptance.py

@@ -456,6 +456,30 @@ def test_delete_device_removed(seeded_client):
 # Full round-trip
 # ------------------------------------------------------------------ #
 
+def test_add_device_with_type(client):
+    resp = client.post("/device/add",
+                       data={"name": "TV Remote", "battery_slots": "2", "device_type": "Remote Control"},
+                       follow_redirects=True)
+    assert resp.status_code == 200
+    assert b"TV Remote" in resp.data
+
+
+def test_device_detail_shows_type(client):
+    client.post("/device/add", data={"name": "Torch", "battery_slots": "1", "device_type": "Flashlight"})
+    resp = client.get("/device/1")
+    assert resp.status_code == 200
+    assert b"Flashlight" in resp.data
+
+
+def test_edit_device_type(client):
+    client.post("/device/add", data={"name": "Torch", "battery_slots": "1"})
+    resp = client.post("/device/1/edit",
+                       data={"name": "Torch", "battery_slots": "1", "device_type": "Flashlight"},
+                       follow_redirects=True)
+    assert resp.status_code == 200
+    assert b"Flashlight" in resp.data
+
+
 def test_add_install_delete_battery(client):
     client.post("/device/add", data={"name": "Gadget", "battery_slots": "1"})
     client.post("/battery/add", data={"brand": "AcmeBrand", "count": "1"})