Show the ports a pane's programs listen on, and go to them - #25

Closes #19.

Summary

Codec asks the kernel which TCP ports the processes under each pane's shell listen on, and shows them wherever they help.

Pane, every second (tick)
  if 3 s passed, or something was printed, or a command started 2 s ago
    ListeningPorts.scan                       (CodecCore, nothing is run)
      ProcessInspector.descendants(shell)     npm → sh → node: not only children
      ProcessInspector.listeningPorts(pid)    proc_pidinfo, sockets in LISTEN
    read the last lines printed for the port's address   (first 20 s only)
    session.listeningPorts = …                → PaneDirectory tells every window

command failed, output kept
  PortConflict.port(inOutput:command:)        EADDRINUSE, "address already in use", …
  PaneDirectory.holder(of: port)              every pane looks afresh
  timeline entry remembers port, program, pane

Where the ports show:

 status bar     ~/code/web   main
+                             ⊕ :3000        click: open in the browser; several: a menu
 right sidebar
-  Commands
+  [Commands | Ports]                        ⇧⌘L / ⇧⌘O
+    Commands row, running   "Listening on :3000"
+    Commands row, failed    "Port 3000 is in use by “node” in Tab 2 › left pane"  [Go to Pane]
+    Ports tab               every port in every window; click: go to its pane;
+                            name a process ("Storefront") for as long as it runs
+Window › Listening Ports     the same list; ⌥ opens in the browser
+command palette              "Go to :3000 — node, Tab 2 › left pane", "Open … in the Browser"
 tab tooltip                 + "Listening on :3000 (node)"
 closing alert               + "“npm” and “node” (listening on :3000) are still running…"
 Explain                     + told who has the port

Differences from the issue: descendants rather than children; a rescan on any output rather than on listen/port/http://; the Ports tab, process names and the Window menu came up while trying it.

Evidence

• Before: no port anywhere in the window; a refused npm run dev showed only its last line.
  After: the chip and "Listening on" row, the refused command naming its holder, and the Ports tab:

  
  
  

• Tests: 592 pass locally (swift test -j 2), 24 of them new: real shells with nc listening, a second pane refused the port, the Ports tab across two windows, naming, the menus and palette; port and address parsing against the messages of Node, Go, Python, Ruby, Rust, Java, nginx, Flask and Django.

• Release build: ARCHS="arm64 x86_64" scripts/build-app.sh release builds (x86_64 arm64).

• Not clicked by hand: the Ports tab's hover buttons, its right-click menu and typing a name in the running app; they're covered by tests and a capture of the editor.

Merge Danger

Door: two-way

Nothing stored changes shape: the timeline's new portConflict is optional, so saved panes from before still load, and reverting only drops it. One new saved key, InspectorTab.

Blast Radius: sidebar

• The right sidebar is now a container with tabs. The tab bar's sidebar button reopens it on the tab it was last on, not always Commands, and the Commands header shows the pane's title instead of the word "Commands".
• Every pane makes a few proc_pidinfo calls every 3 seconds (one call while its shell has started nothing).
• hero.png, commands.png and usual-duration.png were retaken for the new sidebar.
• recordsEachCommandWithItsOutput is flaky on main already (4 of 20 runs there): the test types ahead of the prompt. Not changed here.

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