refactor: uniform validation, fix create form UX, dedupe filter dropdowns

- Remove dead registerValidator (Auth/register.ts), unused since signupValidator
  is the one actually wired to NewAccountController
- computers/create.vue: switch to useForm() + @submit.prevent so the form
  submits on Enter and shows a processing state, matching components/create.vue
- components/edit.vue: drop the 'origin' field, which was never provided by
  the backend (edit() never shared it) and therefore always undefined
- Extract FilterDropdown.vue and reuse it in ComponentsViewer/ComputersViewer,
  removing ~80 lines of duplicated dropdown markup/logic and fixing duplicate
  HTML ids (id="used" appeared twice in ComputersViewer)
- Move MIGRATION_*.md artifacts into docs/migration-history/

inertia/pages/components/edit.vue

@@ -3,14 +3,14 @@ import { reactive } from 'vue'
 import { Link } from '@adonisjs/inertia/vue'
 import { usePage } from '@inertiajs/vue3'
 import CustomSelect from '~/pages/widgets/CustomSelect.vue'
+import type { Component, ComponentType } from '~/pages/types/UITypes'
 
 const { props } = usePage<{
-  component: any
-  types: any[]
-  origin: string
+  component: Component
+  types: ComponentType[]
   errors?: Record<string, string>
 }>()
-const { component, types, origin } = props
+const { component, types } = props
 
 const form = reactive({
   id: component.id,
@@ -18,7 +18,6 @@ const form = reactive({
   price: component.price,
   typeId: component.type.id,
   purchaseDate: component.purchaseDate,
-  origin: origin,
 })
 </script>