Implement porthole v0.1: profiles, supervised open/close, reconnect

Full CLI per spec v0.2 - add/open/close/edit/status/list/remove/wipe/
completions, plus a hidden `__supervise` subcommand that IS the
supervisor process.

- profile.rs: TOML-backed profiles at ~/.config/porthole/profiles/,
  validated -l/-r/-d mapping + --via grammar, atomic writes.
- instance.rs: JSON runtime state at ~/.local/state/porthole/, an
  flock-based lock file that's the source of truth for "is this open"
  (survives a crash/kill -9 without stale-lock cleanup), pid liveness
  checked against /proc rather than trusted from disk.
- supervisor.rs: the __supervise loop - spawns ssh, traps SIGTERM/SIGINT
  into a flag (rather than inferring intent from ssh's exit status),
  classifies failures as fatal/known-transient/unrecognized, backs off
  with a stability-reset, rotates its log.
- ssh.rs: builds the ssh invocation, including splitting --via into a
  -J jump chain plus the mandatory positional target.
- open.rs: the detach/re-exec dance (setsid via pre_exec) and a bounded
  wait for the supervisor to reach Up/Error before open returns, so an
  immediate failure surfaces as a non-zero exit instead of a false
  "opened" - this took a real bug fix during smoke testing, since the
  instance file's initial state (Reconnecting, meaning "attempt in
  flight") was indistinguishable from "already failed once" by state
  alone.
- close.rs: SIGTERM+wait, or SIGKILL the whole process group with
  --force so ssh can't be left orphaned.

Smoke-tested against invalid/unreachable hosts (no real infrastructure
touched): CLI surface, validation errors, add/edit/list/status/remove,
the reconnect/backoff loop with live state transitions, close mid-retry,
edit-while-running's warning, open --all, and wipe. cargo test: 14/14.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/commands/edit.rs

@@ -0,0 +1,31 @@
+use crate::cli::EditArgs;
+use crate::commands::{edits_from_mapping, mapping_is_empty};
+use crate::error::{PortholeError, Result};
+use crate::{instance, profile, ui};
+
+pub fn run(args: EditArgs) -> Result<()> {
+    if mapping_is_empty(&args.mapping) {
+        return Err(PortholeError::NothingToDo(
+            "pass at least one of -l/-r/-d, --via, --user, --identity, --port, --reconnect, \
+             --retry-interval, --backoff-max, --keepalive."
+                .into(),
+        ));
+    }
+
+    let name = profile::normalize(&args.name);
+    let mut p = profile::load(&name)?;
+
+    let edits = edits_from_mapping(&args.mapping);
+    p.apply_edits(&edits)?;
+    profile::save(&p)?;
+
+    // Spec §5.4: edit never restarts a running instance - just warn.
+    if instance::running_pid(&name)?.is_some() {
+        ui::warn(&format!(
+            "'{name}' is currently open; this change won't take effect until the next open/close cycle."
+        ));
+    }
+
+    ui::ok(&format!("Updated profile '{name}'."));
+    Ok(())
+}