feat(vault): create/edit identity ciphers (write path) #67

Job	Run time
cargo-deny	39s
headless build (no TUI / clipboard deps)	29s
vault --version emits §13.2 attribution	34s
test (ubuntu-latest)	30s
rustfmt	13s
test (macos-latest)	41s
cargo-audit	3m 7s
clippy	27s
	6m 40s

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