Plugin tiles: allow full-page size and larger digits

I’ve built a small plugin, Idle Clock: current weather on top, a large clock below, and a tap that returns to the home page. It’s meant as the screen’s resting page. Two limits keep it from working as intended:

1. Full-page plugin tiles The manifest accepts sizes: { full: true }, but the docs say neither the app nor the editor uses it yet. On a 2×3 grid, a size equal to the whole grid only exists as full, so 2×2 is the largest a plugin tile can reach. My request: let the editor offer full for plugin tiles whose manifest sets full: true, the way it does for Tessera’s own full-page tiles.

2. A larger font for digits Font::DIGITS is the largest font a plugin can use, at about 64 px on the standard look. That’s small for a clock or temperature filling half of a 4" screen, and tiny on a 10" panel. The bedside clock tile already draws much larger digits. My request: give plugins access to that digit font, for example as a Font::DIGITS_LARGE (only 0–9 : - ° %, to limit the flash cost), or allow an integer scale on DIGITS.

Nice to have: a tessera::show_page(n) call in the plugin API. Today a tap that should change page has to go through a Home Assistant script and esphome._show_page, which adds a round trip and depends on Home Assistant being reachable.

Tested on a Waveshare ESP32-P4-86 panel running Tessera 0.4.88.