chore: housekeeping and refactoring (bump to 4.7.1)

- Remove unused parameters, dead files, and inaccurate doc.go files
- Extract shared helpers, eliminate duplication
- Rename cheatpath.Cheatpath to cheatpath.Path
- Optimize filesystem walks (WalkDir, skip .git)
- Move sheet name validation to sheet.Validate
- Move integration tests to test/integration/
- Consolidate internal/mock into mocks/
- Move fuzz.sh to test/
- Inline loadSheets helper into command callers
- Extract config.New into its own file
- Fix stale references in HACKING.md and CLAUDE.md
- Restore plan9 build target
- Remove redundant and low-value tests
- Clean up project documentation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/display/faint_test.go

@@ -1,26 +1,20 @@
 package display
 
-import (
-	"testing"
-
-	"github.com/cheat/cheat/internal/config"
-)
+import "testing"
 
 // TestFaint asserts that Faint applies faint formatting
 func TestFaint(t *testing.T) {
 
 	// case: apply colorization
-	conf := config.Config{Colorize: true}
 	want := "\033[2mfoo\033[0m"
-	got := Faint("foo", conf)
+	got := Faint("foo", true)
 	if want != got {
 		t.Errorf("failed to faint: want: %s, got: %s", want, got)
 	}
 
 	// case: do not apply colorization
-	conf.Colorize = false
 	want = "foo"
-	got = Faint("foo", conf)
+	got = Faint("foo", false)
 	if want != got {
 		t.Errorf("failed to faint: want: %s, got: %s", want, got)
 	}