Support reading secret values from stdin or files to handle multiline content like SSH keys, certificates, and config files. New value patterns: - `--value -` reads from stdin - `--value @<path>` reads from file - `--value <text>` uses literal value (backward compatible) File path handling: - Supports tilde expansion for home directory (~/) - Provides clear error messages if file cannot be read Examples: # From stdin cat ~/.ssh/id_ed25519 | tangled spindle secret add \ --repo myrepo --key SSH_KEY --value - # From file tangled spindle secret add --repo myrepo \ --key SSH_KEY --value @~/.ssh/id_ed25519 # Literal value (existing behavior) tangled spindle secret add --repo myrepo \ --key API_KEY --value "my-secret-key" Fixes issue where multiline values were split into multiple arguments by the shell, causing clap parsing errors.