feat(import-export): add tags and recurring expenses support

[audemed44]

Summary

• Export/import tags and recurring expenses as dedicated CSV row types
• Expenses now include pipe-separated tag names in the CSV; auto-generated expenses are exported as plain expense rows to preserve history
• Import follows the correct creation order: tags → categories → recurring → expenses → budgets
• Updated export/import UI to show counts for tags and recurring expenses
• Updated CLAUDE.md with a schema change checklist and import/export format docs
• Updated README.md with tags feature description, recurring processor behaviour, and import/export format table

Test plan

• Export from an instance with tags, recurring expenses, and auto-generated expenses — verify all row types appear in the CSV
• Import the exported CSV into a fresh instance — verify categories, tags, recurring rules, and expenses are recreated correctly
• Confirm auto-generated expenses appear as plain expense rows (no recurringExpenseId reference) in the CSV
• Confirm the recurring processor generates new entries from today onwards after import without duplicating imported expenses
• Verify import of an old CSV (without frequency/startDate/endDate/tags columns) still works for existing row types