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/cheatpath/validate.go

@@ -2,39 +2,15 @@ package cheatpath
 
 import (
 	"fmt"
-	"path/filepath"
-	"strings"
 )
 
-// ValidateSheetName ensures that a cheatsheet name does not contain
-// directory traversal sequences or other potentially dangerous patterns.
-func ValidateSheetName(name string) error {
-	// Reject empty names
-	if name == "" {
-		return fmt.Errorf("cheatsheet name cannot be empty")
+// Validate ensures that the Path is valid
+func (c Path) Validate() error {
+	if c.Name == "" {
+		return fmt.Errorf("cheatpath name cannot be empty")
 	}
-
-	// Reject names containing directory traversal
-	if strings.Contains(name, "..") {
-		return fmt.Errorf("cheatsheet name cannot contain '..'")
+	if c.Path == "" {
+		return fmt.Errorf("cheatpath path cannot be empty")
 	}
-
-	// Reject absolute paths
-	if filepath.IsAbs(name) {
-		return fmt.Errorf("cheatsheet name cannot be an absolute path")
-	}
-
-	// Reject names that start with ~ (home directory expansion)
-	if strings.HasPrefix(name, "~") {
-		return fmt.Errorf("cheatsheet name cannot start with '~'")
-	}
-
-	// Reject hidden files (files that start with a dot)
-	// We don't display hidden files, so we shouldn't create them
-	filename := filepath.Base(name)
-	if strings.HasPrefix(filename, ".") {
-		return fmt.Errorf("cheatsheet name cannot start with '.' (hidden files are not supported)")
-	}
-
 	return nil
 }