Fix tab bar layout and add assets:compile rake task

Prevent the dark mode toggle from wrapping its emoji and label onto
separate lines (white-space: nowrap), and anchor the group tabs to the
bottom of the tab bar (align-self: flex-end) so they connect seamlessly
with the content panel while the toggle aligns to the top.

Add `rake assets:compile` task (migrated from simplecov-html) to build
the compiled JS and CSS from html_frontend/ sources via esbuild, and add
a CI workflow that runs the TypeScript type checker on every push.

Author: sferik

.github/workflows/typecheck.yml

@@ -0,0 +1,18 @@
+name: typecheck
+
+on: [push, pull_request]
+
+jobs:
+  typecheck:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: html_frontend
+    steps:
+      - uses: actions/checkout@v6
+
+      - uses: oven-sh/setup-bun@v2
+
+      - run: bun install
+
+      - run: bun run typecheck

Rakefile

@@ -38,3 +38,29 @@ end
 
 task test: %i[spec cucumber test_html]
 task default: %i[rubocop spec cucumber test_html]
+
+namespace :assets do
+  desc "Compile frontend assets (JS + CSS) using esbuild"
+  task :compile do
+    frontend = File.expand_path("html_frontend", __dir__)
+    outdir = File.expand_path("lib/simplecov/formatter/html_formatter/public", __dir__)
+
+    puts "Compiling assets..."
+
+    # JS: esbuild bundles TypeScript + highlight.js and minifies
+    sh "cd #{frontend} && esbuild src/app.ts --bundle --minify --target=es2015 --outfile=#{outdir}/application.js"
+
+    # CSS: concatenate in order and minify
+    css = %w[
+      assets/stylesheets/reset.css
+      assets/stylesheets/plugins/highlight.css
+      assets/stylesheets/screen.css
+    ].map { |f| File.read(File.join(frontend, f)) }.join("\n")
+
+    IO.popen(%w[esbuild --minify --loader=css], "r+") do |io|
+      io.write(css)
+      io.close_write
+      File.write("#{outdir}/application.css", io.read)
+    end
+  end
+end

html_frontend/assets/stylesheets/screen.css

@@ -258,6 +258,7 @@ abbr.timeago {
 
 .group_tabs {
   display: flex;
+  align-self: flex-end;
   gap: var(--sp-1);
   overflow-x: auto;
 }
@@ -874,6 +875,7 @@ table.file_list .totals-row td {
   font-size: 16px;
   font-family: var(--font-sans);
   cursor: pointer;
+  white-space: nowrap;
   transition: color 0.15s, border-color 0.15s;
 }