Add an All PCs policy scope that excludes servers

The policy builder only offered "Matches everything" (the `true` scope node),
which also targets servers. Authoring an estate-wide policy almost always means
"every PC an operator sits at", and a reboot or script push against a server is
a materially different event.

Adds an `allpcs` scope node that matches every endpoint except those whose
computer type is server-designated. Server designation reads the computer type's
ICON slug, which is nominally a UI hint and is now load-bearing; it was chosen
over matching the type NAME (a site can rename "Server") and over a new isserver
column (needs a migration). It is isolated behind SERVER_ICON so promoting it to
a real flag later is a one-place change.

The `true` node is retained and still matches servers, so existing policies keep
their exact meaning rather than silently re-scoping. It stays visible in the
dropdown only when editing a policy that already uses it; new policies default
to `allpcs`.

Covered by tests/test_plugins/test_computers_policy_allpcs.py, verified against
a planted canary so the server-exclusion assertions are known to bite.

plugins/computers/frontend/views/ConfigurationPoliciesList.vue

@@ -140,7 +140,7 @@ const error = ref('')
 const form = ref(emptyForm())
 
 function emptyForm() {
-  return { name: '', description: '', scopejson: { type: 'true' }, actions: [] }
+  return { name: '', description: '', scopejson: { type: 'allpcs' }, actions: [] }
 }
 
 onMounted(() => loadData())
@@ -221,7 +221,7 @@ function openModal(item = null) {
     form.value = {
       name: item.name || '',
       description: item.description || '',
-      scopejson: item.scopejson ? JSON.parse(JSON.stringify(item.scopejson)) : { type: 'true' },
+      scopejson: item.scopejson ? JSON.parse(JSON.stringify(item.scopejson)) : { type: 'allpcs' },
       actions: (item.actions || []).map(a => ({
         action: a.action, mode: a.mode || 'gate',
         desiredstate: a.desiredstate, params: a.params, intervalminutes: a.intervalminutes

plugins/computers/frontend/views/ScopeNodeEditor.vue

@@ -2,7 +2,8 @@
   <div class="scope-node">
     <div class="scope-node-row">
       <select v-model="node.type" class="form-control scope-type" @change="onTypeChange">
-        <option value="true">Matches everything</option>
+        <option value="allpcs">All PCs (excludes servers)</option>
+        <option v-if="node.type === 'true'" value="true">Matches everything (incl. servers)</option>
         <option value="pctype">PC type is</option>
         <option value="app">App is installed</option>
         <option value="and">ALL of (AND)</option>
@@ -71,20 +72,20 @@ function onTypeChange() {
   delete node.nodes
   delete node.node
   if (node.type === 'and' || node.type === 'or') {
-    node.nodes = [{ type: 'true' }]
+    node.nodes = [{ type: 'allpcs' }]
   } else if (node.type === 'not') {
-    node.node = { type: 'true' }
+    node.node = { type: 'allpcs' }
   }
 }
 
 function addChild() {
-  props.node.nodes.push({ type: 'true' })
+  props.node.nodes.push({ type: 'allpcs' })
 }
 
 function removeChild(index) {
   props.node.nodes.splice(index, 1)
   if (props.node.nodes.length === 0) {
-    props.node.nodes.push({ type: 'true' })
+    props.node.nodes.push({ type: 'allpcs' })
   }
 }
 </script>