Kaia Counter Test v0.3.1 FINAL

Take 3 final adjustment:
- Kaia Counter component as a whole uses a local/system Mincho font stack.
- Success/error messages and button now visually belong to the same component.
- No font files are bundled or redistributed.
- Kaia Spec colors remain #3858A6 × #FFF8EE.
- User-facing issued-state message remains:
  既に発行されているため、発行できません。
- Internal guard details remain undisclosed.
- Existing database, counter value, and issue history are preserved.
- Planet test build; PDF generation is a separate next-stage component.

Shortcode:
[kaia_counter id="counter-test"]
