dsh-theme-firefly: Applying the Firefly Theme to DSH Web UI

dsh-theme-firefly is a DSH Web UI theme plugin (v0.1.2) maintained by Liu-ZA-81. Inspired by Firefly from Honkai: Star Rail, it covers over 100 design tokens and provides wallpapers, a boot animation, firefly particles, background music, and typing sound effects. Install it with `dsh plugin --profile web add dsh-theme-firefly`, then restart DSH web to use it. It supports runtime imports for wallpapers and custom asset builds, and the code is released under the MIT license. Multiple themes are mutually exclusive, and it is recommended to enable only one at a time.