Squashed (migration)

(initial) Align formatting and code style to project standards.
Add live_test.sh: full automated integration suite against a real SSH server
Show [name] for optional positionals, allow filtering import by name too
Fix transfer rough edges: value-name hint, identity warnings, single-profile export
Add transfer subcommand for bulk profile export/import
Harden forced ssh flags: accept-new host keys, block multiplexing, tighten identity auth
release build opts
Standardize error messages, formatting, and code style. Refine --help text for consistency. Update comments for clarity and tone alignment.
Normalize user-facing --help text for tone/format consistency
Show real mapping grammar in --help, make --via repeatable, trim comments
Match vmic's custom top-level --help renderer
Implement porthole v0.1: profiles, supervised open/close, reconnect
Fix --via/-J grammar and --force process-group kill
added .gitignore

src/atomic.rs

@@ -0,0 +1,25 @@
+//! Atomic file writes: write to a sibling temp file, then `rename` over the
+//! target. Matters here specifically for the instance JSON file, which the
+//! supervisor rewrites on every state change while it may be alive for
+//! months; a reader (`status`/`list`) must never observe a half-written
+//! file, and a crash mid-write must never corrupt the last-known-good state.
+
+use std::io::Write;
+use std::path::Path;
+
+pub fn write(path: &Path, contents: &[u8]) -> std::io::Result<()>
+{
+    let tmp = path.with_extension(format!(
+        "{}.tmp.{}",
+        path.extension().and_then(|e| e.to_str()).unwrap_or(""),
+        std::process::id()
+    ));
+
+    {
+        let mut f = std::fs::File::create(&tmp)?;
+        f.write_all(contents)?;
+        f.sync_all()?;
+    }
+
+    std::fs::rename(&tmp, path)
+}