[Bug] PDF/CSV export shows i18n translation keys instead of column names (e.g. "expense.field.payment_account" instead of "Payment Account")

## Description When exporting Expenses to PDF (or CSV), the column headers display raw i18n translation keys instead of the resolved human-readable column names. **Expected headers:** `Payment Account | Reference No | Payment Date | Description | Expense Account | Amount | Line Description` **Actual headers:** `expense.field.payment_account | expense.field.reference_no | expense.field.payment_date | expense.field.description | expense.field.expense_account | expense.field.amount | expense.field.line_description` ## Root cause The translation file at `packages/server/dist/i18n/en/expense.json` correctly maps the keys: ```json { "field.payment_date": "Payment Date", "field.payment_account": "Payment Account", "field.amount": "Amount", ... } ``` But the export code passes the fully-qualified key (`expense.field.payment_account`) to the i18n resolver, which looks it up as-is. Since the JSON file keys don't include the `expense.` namespace prefix (they're just `field.payment_account`), the lookup fails and the raw key is rendered. The i18n namespace prefix (`expense.`) needs to be stripped before the lookup, or the resolver needs to be namespace-aware. ## Steps to reproduce 1. Self-hosted Bigcapital (latest Docker images) 2. Create any expense 3. Go to Expenses list 4. Click Export → PDF (or Print) 5. Observe column headers show `expense.field.payment_account` etc. ## Environment - **Version:** `bigcapitalhq/server:latest` + `bigcapitalhq/webapp:latest` (pulled 2026-04-12) - **Deploy method:** Docker Compose (`docker-compose.prod.yml`) - **OS:** Ubuntu 24.04 - **Language setting:** English - **Gotenberg:** v7 (as specified in the prod compose) ## Screenshots PDF export shows: ``` expense.field.payment_account expense.field.reference_no expense.field.payment_date expense.field.description expense.field.expense_account expense.field.amount expense.field.line_description Branch Owners Funds EXP-011 01 Mar 2026 Massive Stocks API... Software & Subscriptions 1,920.00 Massive API annual... ``` Note: the data rows are correct — only the header row is broken. ## Suggested fix In the expense export service, when resolving column header translations, strip the entity namespace prefix before the i18n lookup. For example: - Current: `i18n.t('expense.field.payment_account')` → lookup fails → renders raw key - Fixed: `i18n.t('field.payment_account', { ns: 'expense' })` → resolves to "Payment Account" Or adjust the i18n resolver to automatically scope lookups by the entity namespace when rendering export templates.