feat: implement modular numbered script system

- Add scripts/ directory with numbered execution pattern
- Create 00-check-dependencies.sh for requirement validation
- Create 10-backup-files.sh for conflict handling
- Create 20-setup-stow.sh for symlink creation
- Create 90-post-install.sh for cleanup tasks
- Add scripts/utils.sh with colored logging functions
- Update install.sh to auto-discover and execute numbered scripts
- Remove hardcoded logic in favor of flexible script discovery

Benefits:
- Clean separation of concerns (each script has one job)
- Numbered execution order (SSH/systemd convention)
- Colored output for better UX
- Easy to extend with additional scripts
- Same entry point for all branches

scripts/10-backup-files.sh

@@ -0,0 +1,41 @@
+#!/bin/bash
+# scripts/10-backup-files.sh - Backup existing files that would conflict
+
+set -euo pipefail
+
+# Source utilities
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+source "$SCRIPT_DIR/utils.sh"
+
+backup_files() {
+    local dotfiles_dir="$1"
+    
+    log_info "Checking for file conflicts..."
+    
+    # Files that might conflict with stow
+    local files_to_check=(.bashrc .bash_aliases .inputrc .gitconfig)
+    local backed_up=()
+    
+    for file in "${files_to_check[@]}"; do
+        if [ -f "$HOME/$file" ] && [ ! -L "$HOME/$file" ]; then
+            log_warning "Backing up existing file: $HOME/$file -> $HOME/${file}.bak"
+            mv "$HOME/$file" "$HOME/${file}.bak"
+            backed_up+=("$file")
+        fi
+    done
+    
+    if [ ${#backed_up[@]} -gt 0 ]; then
+        log_info "Backed up ${#backed_up[@]} file(s): ${backed_up[*]}"
+    else
+        log_info "No file conflicts found"
+    fi
+}
+
+# Run if called directly
+if [[ "${BASH_SOURCE[0]}" == "${0}" ]]; then
+    if [ $# -ne 1 ]; then
+        log_error "Usage: $0 <dotfiles_directory>"
+        exit 1
+    fi
+    backup_files "$1"
+fi