feat(reports): date-range daily sales export with per-tax-rate summary for accountants #1335

Parent: #830 (S1 accountant export). Verified against main @ 8e39053.

Problem

Accountants want one file per month or period. Today owners have to download one business day at a time.

Current behavior (verified)

• GET /reports/daily-sales/export (main/routes/reports.ts ~L1410) exports a single business day. docs/reference/daily-sales-export.md says "One business day at a time (no multi-day ranges)" and "No tips".
• The export already has orders, items, a payments part with card transaction ids (feat(payments): card transaction id & export #1233), service and packaging charge totals, and ingredient cost and margin (feat: add ingredient cost tracking and profitability reporting #1332).

Decisions (made)

• Add from / to business-date parameters (inclusive, store timezone, business-day cutoff respected), capped at 93 days per request so memory stays bounded.
• Keep the existing single-day call working unchanged (date=).
• Add a per-tax-rate summary sheet: taxable base, tax and gross per rate per day. This is what accountants file from.

Scope

• main/services/daily-sales-export.ts, daily-sales-export-files.ts, the route in reports.ts, and the date-range picker in the dashboard export UI.
• Update docs/reference/daily-sales-export.md in the same PR (replace the "one day" limitation).

Out of scope: accounting-software specific formats (Tally, QuickBooks, Xero) and tips (#364).

Acceptance criteria

• A range export over N days equals the sum of N single-day exports (orders, payments, tax).
• Ranges over 93 days, or with to < from, return 400 with a clear message.
• The tax summary sheet totals equal the tax totals of the orders sheet.
• CSV parts and xlsx sheets are consistent.

Verification

• tests/daily-sales-export.test.ts: add range equivalence, cutoff boundary and cap tests.
• npm run lint && npm test