feat(ui): constrain add-account to a root-type dropdown + sub-path

Free-typing the full hierarchical name let admins fat-finger the parent
(wrong/invalid root). Replace the single name field with a required
Account Type select (the 5 valid roots, mirroring _VALID_ACCOUNT_PREFIXES)
plus a sub-account input, a live 'Will create: ...' preview, and
per-segment validation (each part must be a capitalized Beancount
account component). The root prefix is now structurally guaranteed valid.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

static/js/index.js

@@ -71,7 +71,8 @@ window.app = Vue.createApp({
       },
       addAccountDialog: {
         show: false,
-        name: '',
+        rootType: 'Expenses',
+        subPath: '',
         description: '',
         loading: false
       },
@@ -292,6 +293,16 @@ window.app = Vue.createApp({
       })
       return options
     },
+    accountRootTypes() {
+      // The five Beancount root account types — the only valid parents.
+      // Mirrors the server's _VALID_ACCOUNT_PREFIXES.
+      return ['Assets', 'Liabilities', 'Equity', 'Income', 'Expenses']
+    },
+    addAccountFullName() {
+      const sub = (this.addAccountDialog.subPath || '').trim().replace(/^:+|:+$/g, '')
+      if (!this.addAccountDialog.rootType || !sub) return ''
+      return `${this.addAccountDialog.rootType}:${sub}`
+    },
     userOptions() {
       const options = []
       this.users.forEach(user => {
@@ -573,17 +584,26 @@ window.app = Vue.createApp({
       }
     },
     showAddAccountDialog() {
-      this.addAccountDialog.name = ''
+      this.addAccountDialog.rootType = 'Expenses'
+      this.addAccountDialog.subPath = ''
       this.addAccountDialog.description = ''
       this.addAccountDialog.show = true
     },
     async submitAddAccount() {
-      const name = (this.addAccountDialog.name || '').trim()
-      const validPrefixes = ['Assets:', 'Liabilities:', 'Equity:', 'Income:', 'Expenses:']
-      if (!validPrefixes.some(p => name.startsWith(p))) {
+      const name = this.addAccountFullName
+      if (!name) {
+        this.$q.notify({type: 'warning', message: 'Enter a sub-account name'})
+        return
+      }
+      // Each segment under the root must be a valid Beancount account
+      // component: start with an uppercase letter, then letters/digits/hyphens.
+      const badSegment = name.split(':').slice(1).find(
+        seg => !/^[A-Z][A-Za-z0-9-]*$/.test(seg)
+      )
+      if (badSegment !== undefined) {
         this.$q.notify({
           type: 'warning',
-          message: `Account name must start with one of: ${validPrefixes.join(', ')}`
+          message: `Invalid segment "${badSegment}" — each part must start with a capital letter (letters, digits, hyphens only)`
         })
         return
       }

templates/libra/index.html

@@ -1251,15 +1251,28 @@
     <q-form @submit="submitAddAccount" class="q-gutter-md">
       <div class="text-h6 q-mb-md">Add Account</div>
 
+      <q-select
+        filled
+        dense
+        v-model="addAccountDialog.rootType"
+        :options="accountRootTypes"
+        label="Account Type *"
+        hint="Top-level category — the only valid parents"
+      ></q-select>
+
       <q-input
         filled
         dense
-        v-model.trim="addAccountDialog.name"
-        label="Account Name *"
-        placeholder="e.g., Expenses:Services:Domain"
-        hint="Full hierarchical name. Must start with Assets:, Liabilities:, Equity:, Income: or Expenses:"
+        v-model.trim="addAccountDialog.subPath"
+        label="Sub-account *"
+        placeholder="e.g., Vehicle:Gas"
+        hint="Path under the type. Use ':' to nest; capitalize each part."
       ></q-input>
 
+      <div v-if="addAccountFullName" class="text-caption text-grey">
+        Will create: <span class="text-weight-medium">{% raw %}{{ addAccountFullName }}{% endraw %}</span>
+      </div>
+
       <q-input
         filled
         dense
@@ -1279,7 +1292,7 @@
           color="primary"
           type="submit"
           :loading="addAccountDialog.loading"
-          :disable="!addAccountDialog.name"
+          :disable="!addAccountFullName"
         >
           Create Account
         </q-btn>