Flexible budget import with auto-account creation and text-based account numbers

Change account_number from INTEGER to VARCHAR(50) to support segmented codes
like 30-3001-0000 used by real HOA accounting systems. Budget CSV import now:
- Auto-creates income/expense accounts from CSV when they don't exist
- Infers account_type and fund_type from account number prefix conventions
- Parses currency-formatted values ($48,065.21, $(13,000.00), $-, etc.)
- Reports created accounts back to the user

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/pages/accounts/AccountsPage.tsx

@@ -61,7 +61,7 @@ const ACCOUNT_TYPE_OPTIONS = [
 
 interface Account {
   id: string;
-  account_number: number;
+  account_number: string;
   name: string;
   description: string;
   account_type: string;
@@ -93,7 +93,7 @@ interface Investment {
 
 interface TrialBalanceEntry {
   id: string;
-  account_number: number;
+  account_number: string;
   name: string;
   account_type: string;
   fund_type: string;
@@ -158,7 +158,7 @@ export function AccountsPage() {
   // ── Create / Edit form ──
   const form = useForm({
     initialValues: {
-      accountNumber: 0,
+      accountNumber: '',
       name: '',
       description: '',
       accountType: 'expense',
@@ -176,7 +176,7 @@ export function AccountsPage() {
       withdrawFromPrimary: true,
     },
     validate: {
-      accountNumber: (v, values) => isInvestmentType(values.accountType) ? null : (v > 0 ? null : 'Required'),
+      accountNumber: (v, values) => isInvestmentType(values.accountType) ? null : (v.trim().length > 0 ? null : 'Required'),
       name: (v) => (v.length > 0 ? null : 'Required'),
       principal: (v, values) => isInvestmentType(values.accountType) ? (v > 0 ? null : 'Required') : null,
     },
@@ -609,7 +609,7 @@ export function AccountsPage() {
 
             {!isInvestmentType(form.values.accountType) && (
               <>
-                <NumberInput label="Account Number" required {...form.getInputProps('accountNumber')} />
+                <TextInput label="Account Number" placeholder="e.g. 4000 or 40-4007-0000" required {...form.getInputProps('accountNumber')} />
                 <TextInput label="Description" {...form.getInputProps('description')} />
                 {editing && (
                   <Select