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>

backend/src/modules/accounts/dto/create-account.dto.ts

@@ -1,10 +1,10 @@
-import { IsString, IsInt, IsOptional, IsBoolean, IsIn, IsUUID } from 'class-validator';
+import { IsString, IsOptional, IsBoolean, IsIn, IsUUID } from 'class-validator';
 import { ApiProperty } from '@nestjs/swagger';
 
 export class CreateAccountDto {
-  @ApiProperty({ example: 6600 })
-  @IsInt()
-  accountNumber: number;
+  @ApiProperty({ example: '6600' })
+  @IsString()
+  accountNumber: string;
 
   @ApiProperty({ example: 'Equipment Repairs' })
   @IsString()