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/sheets/load_test.go

@@ -5,22 +5,22 @@ import (
 	"testing"
 
 	"github.com/cheat/cheat/internal/cheatpath"
-	"github.com/cheat/cheat/internal/mock"
+	"github.com/cheat/cheat/mocks"
 )
 
 // TestLoad asserts that sheets on valid cheatpaths can be loaded successfully
 func TestLoad(t *testing.T) {
 
 	// mock cheatpaths
-	cheatpaths := []cheatpath.Cheatpath{
+	cheatpaths := []cheatpath.Path{
 		{
 			Name:     "community",
-			Path:     path.Join(mock.Path("cheatsheets"), "community"),
+			Path:     path.Join(mocks.Path("cheatsheets"), "community"),
 			ReadOnly: true,
 		},
 		{
 			Name:     "personal",
-			Path:     path.Join(mock.Path("cheatsheets"), "personal"),
+			Path:     path.Join(mocks.Path("cheatsheets"), "personal"),
 			ReadOnly: false,
 		},
 	}
@@ -54,7 +54,7 @@ func TestLoad(t *testing.T) {
 func TestLoadBadPath(t *testing.T) {
 
 	// mock a bad cheatpath
-	cheatpaths := []cheatpath.Cheatpath{
+	cheatpaths := []cheatpath.Path{
 		{
 			Name:     "badpath",
 			Path:     "/cheat/test/path/does/not/exist",