Agent DX improvements:
- Input hardening: date validation, account name validation (path traversal,
  control chars, percent-encoding), field name validation, positive int check
- --fields on ALL read commands (not just transactions)
- --limit on ALL read commands
- Schema introspection includes per-command field lists
- 36 tests (up from 20)

Renamed: @howells/starling → @howells/starlingcli, binary: starlingcli