feat/tweakcn-theme-import — bake tweakcn themes into projects at build time

[Shewart]

Build-time (not runtime) integration with tweakcn.com theme URLs.

Ships a shellui theme apply <tweakcn-url> CLI subcommand that fetches the theme JSON and rewrites the user's input.css (:root and .dark blocks). Tailwind then compiles the theme into their app.css during dotnet build. No runtime dependency on tweakcn, works offline, exactly-what-you-see is exactly-what-ships.

Scope

• shellui theme apply <url> — fetch tweakcn theme, rewrite input.css :root/.dark blocks
• shellui theme apply <url> --emit-override <path> — for Path A/D users, write an override CSS file (they link it after shellui-all.css)
• shellui theme init <url> — combined init + apply (chain during setup)
• shellui theme update — refresh from last-used URL
• shellui.theme.lock — records source URL + hash for reproducible re-applies
• Extend the four install-path READMEs in shellui-installation-tests/ with theme-apply examples
• New test project path-c-cli-tweakcn/ — end-to-end demo

Why not runtime fetch?

Considered a ShellUI.applyTweakcnTheme(url) JS helper that fetches at page load. Trade-offs made runtime a bad default:

• Flash of wrong theme (FOUT)
• Runtime dep on tweakcn.com availability
• Doesn't work offline / airgapped / CI
• Extra HTTP round-trip on every page load

Build-time bake gives the user exactly what they want ("CSS shipped, exactly what user wants") without those costs. Runtime helper can ship as an opt-in later if there's demand.

Depends on

feat/nuget-precompiled-bundle — merges the precompiled CSS pipeline this feature layers onto.