feat: support tracking categories on manual journals

[rathga]

Problem

Manual journal lines cannot carry Xero tracking categories through this MCP server. The write path silently discards tracking, and the read serializer never prints it — even though the xero-node ManualJournalLine type supports it and the API returns it. The original author left explicit placeholders:

src/handlers/create-xero-manual-journal.handler.ts: // TODO: tracking can be added here
src/handlers/update-xero-manual-journal.handler.ts: // TODO: tracking can be added here
src/tools/create/create-manual-journal.tool.ts:     // TODO: TODO: tracking can be added here
src/tools/update/update-manual-journal-tool.ts:     // TODO: TODO: tracking can be added here

This matters for anyone who tracks journal lines by category (e.g. per-property or per-department) during reconciliation — the codes simply don't come through.

Changes

• Shared schema: extract the invoice trackingSchema ({ name, option, trackingCategoryID }) into src/helpers/tracking-schema.ts and reuse it across create-invoice, update-invoice, and both manual-journal tools — removing the existing duplicated copy in the two invoice tools.
• Write: add tracking (max 2 per line) to the create/update manual-journal line schemas and forward it through both handlers to the Xero API.
• Read: add formatTracking, which renders a line's tracking as readable category/option text (omitting cleanly when absent), and use it in the list-manual-journals serializer and the create success response. The raw array is never printed (avoids the [object Object] pitfall).
• Bug fix: the create success response previously stringified its line array to [object Object],[object Object] — it never rendered line details at all. It now joins lines to text, matching the list serializer.
• Tests: add Vitest coverage for formatTracking.

Verification

Verified end-to-end against a real Xero tenant: created a draft manual journal with tracking on each line, read it back (codes appear), updated the tracking and re-read (new codes appear), and confirmed no [object Object] leaks. npm run lint and npm test pass.

Notes

• Does not touch src/helpers/format-line-item.ts, so it does not collide with PR Format line item tracking values #178 (invoice/bank-tx tracking formatting).
• Bank transactions also lack tracking — left as a separate follow-up.

🤖 Generated with Claude Code