feat: update acronym to 'Hushing' and fix backup creation bug

- Update SHUSH acronym from 'Hiding' to 'Hushing' (better reflects removal)
- Fix critical error handling bug in file backup creation using io.Copy
- Remove golangci-lint references from Makefile and CLAUDE.md
- Update README, LLM guide, and CLI description with new acronym
- Create TASKS.md to track project improvements

internal/guide/guide.go

@@ -4,6 +4,7 @@ import "fmt"
 
 func Show() {
 	fmt.Print(`# Shush CLI - LLM Guide
+**S**loppily **H**ushing **U**nwanted **S**ource-code **H**eavy (comments)
 
 ## Overview
 Shush is a fast comment removal tool for source code files using in-memory processing.