feat: add account management tools (create, update, archive)

[sbs44]

Summary

Adds three new MCP tools for managing Xero chart of accounts:

• create-account — Create accounts with name, code, type, and optional description, taxType, and bankAccountNumber
• update-account — Update account fields including name, code, type, description, taxType, currencyCode, enablePaymentsToAccount, showInExpenseClaims, reportingCode, reportingCodeName, and addToWatchlist
• archive-account — Convenience tool to archive an account by setting its status to ARCHIVED via updateAccount()

All three tools return a deep link to view the account in Xero.

Changes

New files (6):

• src/handlers/create-xero-account.handler.ts
• src/handlers/update-xero-account.handler.ts
• src/handlers/archive-xero-account.handler.ts
• src/tools/create/create-account.tool.ts
• src/tools/update/update-account.tool.ts
• src/tools/update/archive-account.tool.ts

Modified files (4):

• src/consts/deeplinks.ts — added accountDeepLink()
• src/helpers/get-deeplink.ts — added ACCOUNT to DeepLinkType enum and switch
• src/tools/create/index.ts — registered CreateAccountTool
• src/tools/update/index.ts — registered UpdateAccountTool and ArchiveAccountTool

Design decisions

• archive-account as a dedicated tool rather than a flag on update-account, since archiving is a distinct user intent
• archive-account lives in src/tools/update/ since it's implemented as an updateAccount() call under the hood
• create-account is intentionally lean (core fields only) — niche fields like reportingCode can be set via update-account after creation
• All handlers and tools follow existing codebase patterns exactly