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/config/validate_test.go

@@ -14,8 +14,8 @@ func TestValidateCorrect(t *testing.T) {
 		Colorize:  true,
 		Editor:    "vim",
 		Formatter: "terminal16m",
-		Cheatpaths: []cheatpath.Cheatpath{
-			cheatpath.Cheatpath{
+		Cheatpaths: []cheatpath.Path{
+			cheatpath.Path{
 				Name:     "foo",
 				Path:     "/foo",
 				ReadOnly: false,
@@ -38,8 +38,8 @@ func TestInvalidateMissingEditor(t *testing.T) {
 	conf := Config{
 		Colorize:  true,
 		Formatter: "terminal16m",
-		Cheatpaths: []cheatpath.Cheatpath{
-			cheatpath.Cheatpath{
+		Cheatpaths: []cheatpath.Path{
+			cheatpath.Path{
 				Name:     "foo",
 				Path:     "/foo",
 				ReadOnly: false,
@@ -71,19 +71,28 @@ func TestInvalidateMissingCheatpaths(t *testing.T) {
 	}
 }
 
-// TestMissingInvalidFormatters asserts that configs which contain invalid
+// TestInvalidateInvalidFormatter asserts that configs which contain invalid
 // formatters are invalidated
-func TestMissingInvalidFormatters(t *testing.T) {
+func TestInvalidateInvalidFormatter(t *testing.T) {
 
-	// mock a config
+	// mock a config with a valid editor and cheatpaths but invalid formatter
 	conf := Config{
-		Colorize: true,
-		Editor:   "vim",
+		Colorize:  true,
+		Editor:    "vim",
+		Formatter: "html",
+		Cheatpaths: []cheatpath.Path{
+			cheatpath.Path{
+				Name:     "foo",
+				Path:     "/foo",
+				ReadOnly: false,
+				Tags:     []string{},
+			},
+		},
 	}
 
-	// assert that no errors are returned
+	// assert that the config is invalidated due to the formatter
 	if err := conf.Validate(); err == nil {
-		t.Errorf("failed to invalidate config without formatter")
+		t.Errorf("failed to invalidate config with invalid formatter")
 	}
 }
 
@@ -96,14 +105,14 @@ func TestInvalidateDuplicateCheatpathNames(t *testing.T) {
 		Colorize:  true,
 		Editor:    "vim",
 		Formatter: "terminal16m",
-		Cheatpaths: []cheatpath.Cheatpath{
-			cheatpath.Cheatpath{
+		Cheatpaths: []cheatpath.Path{
+			cheatpath.Path{
 				Name:     "foo",
 				Path:     "/foo",
 				ReadOnly: false,
 				Tags:     []string{},
 			},
-			cheatpath.Cheatpath{
+			cheatpath.Path{
 				Name:     "foo",
 				Path:     "/bar",
 				ReadOnly: false,
@@ -127,14 +136,14 @@ func TestInvalidateDuplicateCheatpathPaths(t *testing.T) {
 		Colorize:  true,
 		Editor:    "vim",
 		Formatter: "terminal16m",
-		Cheatpaths: []cheatpath.Cheatpath{
-			cheatpath.Cheatpath{
+		Cheatpaths: []cheatpath.Path{
+			cheatpath.Path{
 				Name:     "foo",
 				Path:     "/foo",
 				ReadOnly: false,
 				Tags:     []string{},
 			},
-			cheatpath.Cheatpath{
+			cheatpath.Path{
 				Name:     "bar",
 				Path:     "/foo",
 				ReadOnly: false,