fix(cli): suppress terminal echo for interactive secret prompts #103

Job	Run time
vault --version emits §13.2 attribution	40s
rustfmt	13s
test (macos-latest)	1m 21s
cargo-audit	3m 3s
test (ubuntu-latest)	47s
headless build (no TUI / clipboard deps)	31s
REUSE lint	13s
clippy	33s
cargo-deny	40s
	8m 1s

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