feat(cli): full AI agent support — new commands, options, and unset flags

[StevenACZ]

Summary

• Add transfers update and loans update commands (backend already supports PUT endpoints)
• Add shared body-builder.ts utility with --no-<field> → null unset support
• Expand all create/update commands to expose every backend-supported field
• Add --currency filter to stats commands
• Fix frequency choices: MONTHLY|YEARLY (remove undocumented WEEKLY)
• Bump version to 0.2.0

Motivation

AI agents managing finances via CLI were blocked by:

1. Cannot unset optional fields (e.g., accountId on subscriptions)
2. Missing fields (billingDay, currency, icon, etc.) — AI had to bypass CLI and call API directly
3. No transfers update or loans update commands
4. No stats currency filtering

New capabilities

# Unset optional fields
lucas subscriptions update <id> --no-account-id
lucas transactions update <id> --no-category-id

# New commands
lucas transfers update <id> --amount 1500 --exchange-rate 3.75
lucas loans update <id> --name "Auto Loan" --interest-rate 5.5

# Full subscription creation (was missing billing-day, currency)
lucas subscriptions create --name "Claude Max" --amount 100 --currency USD --billing-day 4 --frequency MONTHLY

# Stats with currency filter
lucas stats summary --currency USD

Test plan

• bun run typecheck — PASS
• bun run lint — PASS (0 errors)
• bun run build — PASS (107KB bundle)
• All 8 updated commands verified via --help
• Smoke test: lucas auth status and lucas stats summary --currency USD against production

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