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

[UnbreakableMJ]

Problem

vault login / vault unlock echoed the master password in clear text as it was typed — visible on screen and in scrollback. The same flaw affected every other interactive secret prompt: the PIN, the add/edit login password, the card number/CVV, and the identity SSN/passport/license. Separately, the master-password path read stdin until EOF, so a typed password sat at the cursor until Ctrl-D instead of submitting on Enter.

Fix

• Add a NoEcho RAII guard over rustix::termios that clears terminal ECHO for the duration of every interactive secret read and restores the prior attributes on drop — including on early return / panic.
• rustix was already in the dependency tree transitively (via secmem-proc), so no new crate is added and the crate keeps #![forbid(unsafe_code)] (rustix is unsafe-free by design).
• Interactive secret entry now submits on Enter (reads a single line) instead of reading until EOF.
• Piped / redirected input is unchanged — pass show | vault login still reads the whole stream, preserving the "stdin consumed → 2FA from /dev/tty" design.
• Non-secret prompts still echo by design: the register server picker, account email, and the ephemeral authenticator (TOTP) code.

Verification

Full just ci set is green: fmt, clippy -D warnings (--all-features, all 9 crates), test --workspace --all-targets (75 passed, 0 failed), headless, version-gate, deny, audit, reuse.

Verified live through a pseudo-terminal driving vault login: the prompt appears, and the typed secret is absent from all terminal output.

---- raw pty capture (repr) ----
'Master password: \r\nvault: started vault-agent (pid ...)\r\n'
prompt shown : True
secret leaked: False
RESULT: PASS — password prompt shown, typed secret NOT echoed

🤖 Generated with Claude Code