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>

Cargo.toml

@@ -0,0 +1,30 @@
+[package]
+name        = "porthole"
+version     = "0.1.0"
+edition     = "2021"
+description = "Create and manage named SSH port forwards."
+license     = "AGPL-3+"
+
+[[bin]]
+name = "porthole"
+path = "src/main.rs"
+
+[dependencies]
+clap          = { version = "4", features = ["derive"] }
+clap_complete = "4"
+
+thiserror = "^2"
+dirs      = "6"
+
+serde      = { version = "1", features = ["derive"] }
+serde_json = "1"
+toml       = "0.8"
+
+libc = "0.2"
+
+# Keep panics from corrupting a partially-written state file - abort is
+# fine for a CLI/supervisor as there's no long-lived in-process state to
+# unwind (state lives on disk and is written atomically, see src/atomic.rs).
+[profile.release]
+panic = "abort"
+lto   = true