Fix floor persistence and improve movement detection

- Store floor assignments in SQLite database for persistence
- Floor now saves correctly for live-tracked BT devices
- Add statistical movement detection (5-sample average + stddev)
- Require 1.5m + 2σ deviation to mark device as moving
- Reduces false positives from RSSI noise/fluctuations
- Add /api/device/floors endpoint for bulk floor retrieval

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

src/rf_mapper/database.py

@@ -75,6 +75,7 @@ class DeviceDatabase:
                 total_observations INTEGER DEFAULT 0,
                 custom_label TEXT,  -- User-assigned name
                 is_favorite INTEGER DEFAULT 0,
+                assigned_floor INTEGER,  -- User-assigned floor
                 notes TEXT,
                 created_at TEXT DEFAULT CURRENT_TIMESTAMP,
                 updated_at TEXT DEFAULT CURRENT_TIMESTAMP
@@ -160,6 +161,12 @@ class DeviceDatabase:
         cursor.execute("CREATE INDEX IF NOT EXISTS idx_movement_device ON movement_events(device_id, timestamp)")
         cursor.execute("CREATE INDEX IF NOT EXISTS idx_alerts_type ON alerts(alert_type, acknowledged)")
 
+        # Add assigned_floor column if it doesn't exist (migration for existing DBs)
+        try:
+            cursor.execute("ALTER TABLE devices ADD COLUMN assigned_floor INTEGER")
+        except sqlite3.OperationalError:
+            pass  # Column already exists
+
         conn.commit()
 
     def record_scan(self, scan_id: str, timestamp: str, location_label: str,
@@ -463,6 +470,34 @@ class DeviceDatabase:
         """, (1 if is_favorite else 0, device_id))
         conn.commit()
 
+    def set_device_floor(self, device_id: str, floor: Optional[int]):
+        """Set assigned floor for a device"""
+        conn = self._get_connection()
+        cursor = conn.cursor()
+
+        cursor.execute("""
+            UPDATE devices SET assigned_floor = ?, updated_at = CURRENT_TIMESTAMP
+            WHERE device_id = ?
+        """, (floor, device_id))
+        conn.commit()
+
+    def get_device_floor(self, device_id: str) -> Optional[int]:
+        """Get assigned floor for a device"""
+        conn = self._get_connection()
+        cursor = conn.cursor()
+
+        cursor.execute("SELECT assigned_floor FROM devices WHERE device_id = ?", (device_id,))
+        row = cursor.fetchone()
+        return row['assigned_floor'] if row else None
+
+    def get_all_device_floors(self) -> dict:
+        """Get all device floor assignments as a dict"""
+        conn = self._get_connection()
+        cursor = conn.cursor()
+
+        cursor.execute("SELECT device_id, assigned_floor FROM devices WHERE assigned_floor IS NOT NULL")
+        return {row['device_id']: row['assigned_floor'] for row in cursor.fetchall()}
+
     def get_recent_activity(self, hours: int = 24) -> dict:
         """Get activity summary for the last N hours"""
         conn = self._get_connection()