Replace all AU-specific workaround code with v2 API calls via
PayrollAuV2Api. This aligns AU with NZ/UK — all three regions now use
the same v2 endpoint patterns.

Changes per handler:
- approve: remove GET-then-PUT status workaround, call approveTimesheet
- revert: remove GET-then-PUT status workaround, call revertTimesheet
- delete: remove AU error block, call deleteTimesheet (previously unsupported)
- create: remove array wrapping, use single-object createTimesheet
- add-line: remove GET-append-PUT workaround, call createTimesheetLine
- update-line: remove earningsRateID matching, call updateTimesheetLine by ID
- get: call getTimesheet via v2 client
- list: remove AU-only params (where/order/ifModifiedSince), use v2 params

Breaking input changes for AU callers:
- numberOfUnits is now a single number (not array) with a date per line
- payrollCalendarID is now required on create
- timesheetLineID is now required on update-line

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

New handler, tool, and tests for DELETE /timesheets/{id}/lines/{lineId}.
Previously this operation had no MCP tool. Supports AU (via
PayrollAuV2Api), NZ, and UK.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

New tools:
- list-payroll-calendars: shows pay calendar names, types, and upcoming
  payment dates. AU uses payrollAUApi.getPayrollCalendars (v1), NZ/UK
  use getPayRunCalendars.
- list-earnings-rates: shows earnings rate IDs, names, and types needed
  for creating timesheet lines. AU uses payrollAUApi.getPayItems (v1)
  and extracts the earningsRates array, NZ/UK use getEarningsRates.

Both tools support AU, NZ, and UK with region auto-detection.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>