fix(dashboard): add explicit @source for Tailwind v4 detection

Tailwind v4's default source detection walks the nearest .git and
collects tracked files via git ls-files. When the dashboard sources
sit inside a gitignored subtree of an ancestor repo (e.g. the default
marketplace install path ~/.claude/plugins/cache/, which is ignored by
~/.claude/.gitignore), detection returns 0 files and the Oxide engine
skips all utility generation — the dashboard renders unstyled.

Adding explicit @source directives is the supported Tailwind v4 escape
hatch and is a no-op for installs where automatic detection works.

Verified: built CSS bundle jumps from ~9 KB to ~55 KB and utility
classes (.flex, .grid, .absolute, .w-full, .h-full) are present.

Fixes #179

understand-anything-plugin/packages/dashboard/src/index.css

@@ -1,4 +1,6 @@
 @import "tailwindcss";
+@source "./**/*.{ts,tsx,js,jsx,html}";
+@source "../index.html";
 
 @theme {
   /* Base */