Japi Base v0.2 — extended keyboard driver

Built from master a489b81 (hardware-verified).

New since v0.1 — extended keyboard driver (additive, no regressions):

• Shift / Ctrl / Ctrl+Shift + navigation keys now emit distinct codes
  (editor selection & vertical block select).
• Left-Alt + letter = menu accelerator codes (Turbo-Pascal style).
• AltGr and the keyboard layout are unchanged.

Flash: hold BOOTSEL while plugging in the Pico 2, copy japi_base.uf2
onto the RP2350 drive. Demo unchanged (Showcase / Balls / Starry Night
/ API).