feat(11.1-02): add the documentation theme, chroma highlighting and docs:serve

- WinterCMS-style shell: header with search and theme toggle, grouped
  sidebar, on-page TOC, pager, page actions, callouts, heading
  permalinks, footer and a 404 page
- fenced code highlighted at build time by chroma/v2 into tok-* classes,
  with a copy button; no inline script, style or handler
- vendored DM Sans/DM Mono fonts and Lucide icons with their licences
- client-side search over search-index.json built with textContent only
- summer docs:serve builds into a temp dir, serves on loopback by default,
  returns 404.html with status 404 and rebuilds on change

cmd/summer/main_test.go

@@ -19,7 +19,7 @@ func TestToolCommandNames(t *testing.T) {
 	for _, c := range toolCommands() {
 		names = append(names, c.Name)
 	}
-	for _, want := range []string{"build", "make:plugin", "make:model", "make:migration", "make:command", "make:job", "make:admin-controller", "plugin:add", "dev", "migrate", "migrate:rollback", "migrate:status", "serve", "queue:work", "queue:clear", "schedule:run", "parity:broadcasts", "docs:build", "docs:sync"} {
+	for _, want := range []string{"build", "make:plugin", "make:model", "make:migration", "make:command", "make:job", "make:admin-controller", "plugin:add", "dev", "migrate", "migrate:rollback", "migrate:status", "serve", "queue:work", "queue:clear", "schedule:run", "parity:broadcasts", "docs:build", "docs:sync", "docs:serve"} {
 		if !slices.Contains(names, want) {
 			t.Fatalf("missing %s in %v", want, names)
 		}
@@ -36,6 +36,7 @@ func TestToolCommandNames(t *testing.T) {
 		"parity:broadcasts":     {"--flow", "--step", "--ids", "127.0.0.1:8424"},
 		"docs:build":            {"--out", "--src", "--root", "--base-url", "--check"},
 		"docs:sync":             {"--src", "--root"},
+		"docs:serve":            {"--root", "--src", "--base-url", "--addr", "--allow-remote", "127.0.0.1:8088"},
 	}
 	for cmd, wants := range helpWants {
 		var buf bytes.Buffer