feat(vault-tui): per-field reveal/copy in the detail pane (+ card CVV) #83

Job	Run time
cargo-deny	49s
cargo-audit	3m 6s
headless build (no TUI / clipboard deps)	26s
clippy	27s
rustfmt	16s
test (ubuntu-latest)	31s
vault --version emits §13.2 attribution	39s
test (macos-latest)	37s
	6m 51s

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