feat(routing): make routing profiles the sole scheduler policy source

Bootstrap an enabled system-default routing group from the legacy
scheduler config keys on startup, resolve the default ordering config
from that group before falling back to the legacy keys, and stop merging
keep_priority_on_conversion with the legacy flag when a policy is
resolved. Thread the policy-derived ordering config into candidate
preselection so it no longer reads system config independently.

Add per-API-format key priority overrides so a key serving several
formats keeps independent ordering, matching the legacy
global_priority_by_format semantics. Expose keep_priority_on_conversion
in the routing profile editor and read the effective policy in the
model routing preview, monitoring metrics and provider page badge.

frontend/src/views/admin/__tests__/RoutingProfiles.allowed-models.spec.ts

@@ -131,11 +131,31 @@ vi.mock('@/components/ui', async () => {
     },
   })
 
+  const Switch = defineComponent({
+    inheritAttrs: false,
+    props: {
+      modelValue: { type: Boolean, default: false },
+      disabled: Boolean,
+    },
+    emits: ['update:modelValue'],
+    setup(props, { attrs, emit }) {
+      return () => h('button', {
+        ...attrs,
+        type: 'button',
+        role: 'switch',
+        'aria-checked': props.modelValue,
+        disabled: props.disabled,
+        onClick: () => emit('update:modelValue', !props.modelValue),
+      })
+    },
+  })
+
   return {
     Badge: wrapper(),
     Button,
     Card: wrapper('section'),
     Input,
+    Switch,
     Table: wrapper('table'),
     TableBody: wrapper('tbody'),
     TableCard: wrapper(),