feat: Resumable Download Helper and Manifest Preservation

- Route downloads through local cache directory
- Automatically resume interrupted downloads from the byte offset
- `setup_uninstaller_context` checks if a fail had happened. If yes then
  CLI preserves existing manifest instead of wiping it.
- Interruption Signal Traps and Prompts

installers/install_node.sh

@@ -45,8 +45,7 @@ install_nvm() {
 
     local nvm_url="https://github.com/nvm-sh/nvm/archive/refs/tags/${latest_tag}.tar.gz"
     log_info "Downloading NVM from $nvm_url..."
-
-        curl -fsSL "$nvm_url" -o "$TMP_DIR/nvm.tar.gz"
+    download_file "$nvm_url" "$TMP_DIR/nvm.tar.gz"
 
     log_info "Extracting NVM archive directly to $HOME/.nvm (stripping versioned subfolder to keep config generic)..."
     mkdir -p "$HOME/.nvm"