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/installer/template.go

@@ -0,0 +1,58 @@
+package installer
+
+import (
+	"path/filepath"
+	"strings"
+
+	"github.com/cheat/cheat/internal/config"
+)
+
+// cheatsheetDirs returns the community, personal, and work cheatsheet
+// directory paths derived from a config file path.
+func cheatsheetDirs(confpath string) (community, personal, work string) {
+	confdir := filepath.Dir(confpath)
+	community = filepath.Join(confdir, "cheatsheets", "community")
+	personal = filepath.Join(confdir, "cheatsheets", "personal")
+	work = filepath.Join(confdir, "cheatsheets", "work")
+	return
+}
+
+// ExpandTemplate replaces placeholder tokens in the config template with
+// platform-appropriate paths derived from confpath.
+func ExpandTemplate(configs string, confpath string) string {
+	community, personal, work := cheatsheetDirs(confpath)
+
+	// substitute paths
+	configs = strings.ReplaceAll(configs, "COMMUNITY_PATH", community)
+	configs = strings.ReplaceAll(configs, "PERSONAL_PATH", personal)
+	configs = strings.ReplaceAll(configs, "WORK_PATH", work)
+
+	// locate and set a default pager
+	configs = strings.ReplaceAll(configs, "PAGER_PATH", config.Pager())
+
+	// locate and set a default editor
+	if editor, err := config.Editor(); err == nil {
+		configs = strings.ReplaceAll(configs, "EDITOR_PATH", editor)
+	}
+
+	return configs
+}
+
+// CommentCommunity comments out the community cheatpath block in the config
+// template. This is used when the community cheatsheets directory won't exist
+// (either because the user declined to download them, or because the config
+// is being output as an example).
+func CommentCommunity(configs string, confpath string) string {
+	community, _, _ := cheatsheetDirs(confpath)
+
+	return strings.ReplaceAll(configs,
+		"  - name: community\n"+
+			"    path: "+community+"\n"+
+			"    tags: [ community ]\n"+
+			"    readonly: true",
+		"  #- name: community\n"+
+			"  #  path: "+community+"\n"+
+			"  #  tags: [ community ]\n"+
+			"  #  readonly: true",
+	)
+}