fix(install): fold in both reviews of #460

The two reviews on the PR (DeepSeek Harness, then Claude) found one class of
bug twice and a list of smaller ones; all of them land here, each pinned in
test/install-sh-invariants.test.ts and, where it is bash logic, driven in the
bash:3.2 CI step as well.

The Start line the done screen prints is now composed in one place
(start_command_hint) from every non-default value, the same five the exec
branch exports through export_bind_env, so "do not start" under a sub-path or
a custom port no longer prints a bare `codeman web`. The --lan / --tailscale /
env preset paths read ${CODEMAN_PASSWORD:-$EXISTING_PASSWORD}: a flag re-run on
a unit that carried a password used to rewrite it without the password and
with the unauthenticated ack. --password and --port flip RECONFIGURE so they
reach the unit instead of taking the quiet update path, and `install.sh name`
re-syncs the unit's base URL after the mapping is re-added.

Also: the sudo keepalive is ended before the exec into the foreground server
(exec skips the EXIT trap, and the loop keys on $$); Ctrl+C in the HTTPS-toggle
poll is trapped for the poll only and skips Tailscale for the run instead of
killing the installer; uninstall asks before removing a LaunchDaemon this
installer never wrote; a foreign daemon gets a launchctl kickstart hint and the
done screen stops claiming the new build is running; the preflight summary
reads the Tailscale state with a line grep when node is not installed yet; the
LAN security notice uses the configured port; a bare re-run ends on the done
screen; a build failure after a rename names the install.sh tailscale
recovery; TS_JOINED_HERE (written, never read) is gone; the plan doc and
architecture-invariants say what the code does. A minor changeset is included.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

.changeset/f8e1fca3.md

@@ -0,0 +1,5 @@
+---
+'aicodeman': minor
+---
+
+Installer v2. `curl -fsSL https://getcodeman.com/install | bash` now looks at the machine first, asks at most three questions up front (how the dashboard is reached, optionally what to call the machine on your tailnet, whether to run Codeman as a background service), does the install unattended behind progress spinners with the output in `~/.codeman/install.log`, and ends on the URL with a QR code to scan. One consent covers every missing package and sudo asks for your password once. Flags pipe through `bash -s --` (`--tailscale | --lan | --local`, `--name <n> | --no-rename`, `--service | --run | --no-start`, `--yes`, `--password`, `--port`), `install.sh status` prints the URL and the QR code again, and the cloudflared question moved out of the main flow into `install.sh cloudflared`. On the Tailscale route, a `:443` that already belongs to another app gets Codeman under `https://<node>/codeman` (or on a second port) instead of a dead end, the node can be renamed opt-in (`--name`, `install.sh name`, undone by uninstall), and the HTTPS-certificates toggle is polled with the admin page opened for you. Also fixed on the way: the installer's own `npm install` no longer lets the postinstall start a stray server on port 3000 (the service crash-looped on EADDRINUSE while the done screen said "running"), the LAN address comes from the default route rather than the first interface, a hand-written LaunchDaemon on a headless Mac is left alone, a flag re-run keeps an existing dashboard password, and the done screen's start command carries the sub-path and port it was installed with.