fix: remove device_role_source from form params (#110)

- Removed device_role_source assignment in sanitize_device_role/1
- Updated structure.sql to reflect database schema without device_role_source column
- Fixes ERROR 42703 (undefined_column) in production workers

The form was still trying to set device_role_source in params even though
the database column was dropped, causing runtime errors in:
- AgentLatencyEvaluator
- CapacityInsightWorker
- WirelessInsightWorker

All device roles are now manually set with default value 'other'.

Reviewed-on: graham/towerops-web#110

lib/towerops_web/live/device_live/form.ex

@@ -652,17 +652,15 @@ defmodule ToweropsWeb.DeviceLive.Form do
     end
   end
 
-  # Set device_role_source based on whether a role was manually selected
+  # Device role sanitization (auto-inference disabled, all roles are manual)
   defp sanitize_device_role(params) do
     case Map.get(params, "device_role") do
       role when is_binary(role) and role != "" ->
-        Map.put(params, "device_role_source", "manual")
+        params
 
       _ ->
-        # Auto-detect selected (empty string or nil) - clear role, set source to inferred
+        # Empty string or nil - just pass through (schema default will apply)
         params
-        |> Map.put("device_role", nil)
-        |> Map.put("device_role_source", "inferred")
     end
   end