docs: put hc on PATH for non-desktop Herdr clients

hc connect speaks the protocol over stdin/stdout, so clients attach with
ssh <box> hc connect. That failed with "hc: command not found": the binary
installs to /root/.local/bin/herdr-core, which is neither on PATH in a
non-interactive shell nor named hc. The desktop app was unaffected since it
calls the absolute path it installed.

Symlinks both names into /usr/local/bin, restored by the go script, and
records the connection details a mobile client or app builder needs.

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

docs/CHANGELOG.md

@@ -23,6 +23,7 @@
 - **[SERVICE]** Root cause of `core did not start within 5 s` was the hc core socket living under `XDG_RUNTIME_DIR` = `/run/user/0`, which `pam_elogind.so` creates and destroys per login session. Fixed properly with `loginctl enable-linger root`, which keeps that directory alive so every client agrees on the default socket path. An earlier Mac-side `XDG_RUNTIME_DIR` pin fixed the CLI but broke the GUI's plain-ssh "Add a machine"; linger supersedes it and the wrapper is retained but unused.
 - **[SERVICE]** `/boot/config/go` now restores the hc binary **and** re-applies linger at boot, since `/`, `/run` and `/var/lib` are all RAM on Unraid. `sh -n` clean, backups at `/boot/config/go.bak-*`.
 - **[SERVICE]** Corrected a stale `~/.ssh/config` entry that still pointed `unraid` at the deleted node `100.100.208.70` on port 422 — an address and port combination that never worked, since sshd binds only 192.168.10.20 and 192.168.31.250. Replaced with `unraid` (LAN, key, 422) and `unraid-ts` (100.100.208.69, Tailscale SSH, 22). This stale entry was also what the Herdr GUI was listing.
+- **[SERVICE]** Symlinked `/usr/local/bin/hc` and `/usr/local/bin/herdr-core` to the installed binary, and added the links to the go script. `~/.local/bin` is not on PATH in a non-interactive shell and the binary is not named `hc`, so clients using the documented `ssh box hc connect` (the mobile client, anything built on `hc schema`) got "hc: command not found". The desktop app was unaffected because it calls the absolute path it installed.
 - **[SERVICE]** Unraid added to Herdr as the machine `unraid` (`hc` 0.1.17 on the remote). `herdr-core machine add` had been failing with `core did not start within 5 s`: `hc` puts its core socket under `XDG_RUNTIME_DIR`, which on Unraid is `/run/user/0` — a directory elogind creates and destroys per login session, so the socket disappeared the moment the session that started the core ended. The core kept running with an unlinked socket, and `core.log` stayed empty because the failure is client side.
 - **[SERVICE]** Fixed from the Mac only, via `~/.local/bin/herdr-via-unraid`, a `--via` transport that exports `XDG_RUNTIME_DIR=/var/run/herdr-rt` on every connection. Nothing on the server was changed. Uses key auth on 192.168.10.20:422 rather than Tailscale SSH, because `--via` needs a transport that asks nothing and the default tailnet ACL `check` would demand periodic browser re-auth.
 - **[SERVICE]** Reboot caveat: `/` is rootfs (RAM) and `/run` is tmpfs on Unraid, so `/root/.local/bin/herdr-core` is lost at every boot and needs `herdr-core machine update` to restore. A `/boot/config/go` entry now restores it at boot from `/boot/config/herdr/herdr-core` (`install -m 755`, because /boot is FAT32 and carries no execute bit). Applied 2026-11-03, with the go script backed up to `go.bak-20261103-203916` and verified by deleting the binary and running the line by hand. Detail in `docs/14-HERDR-REMOTE-MACHINES.md`.