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>

cmd/cheat/cmd_view.go

@@ -21,8 +21,6 @@ func cmdView(opts map[string]interface{}, conf config.Config) {
 		fmt.Fprintf(os.Stderr, "failed to list cheatsheets: %v\n", err)
 		os.Exit(1)
 	}
-
-	// filter cheatcheats by tag if --tag was provided
 	if opts["--tag"] != nil {
 		cheatsheets = sheets.Filter(
 			cheatsheets,
@@ -42,7 +40,7 @@ func cmdView(opts map[string]interface{}, conf config.Config) {
 				// identify the matching cheatsheet
 				out += fmt.Sprintf("%s %s\n",
 					sheet.Title,
-					display.Faint(fmt.Sprintf("(%s)", sheet.CheatPath), conf),
+					display.Faint(fmt.Sprintf("(%s)", sheet.CheatPath), conf.Color(opts)),
 				)
 
 				// apply colorization if requested