fix(ssh): survive read-only ~/.ssh ControlPath; render sidecar on all host OSes

Coordinated with the pi-extensions ssh-controlmaster fix (picked up at build via
PI_EXTENSIONS_REF=main), this makes `pi --ssh <host>` and `dssh`/`dscp` robust
to a user ~/.ssh/config whose per-host ControlPath points under the read-only
~/.ssh bind-mount (e.g. `ControlPath ~/.ssh/cm/%r@%h:%p`). A system default can
never override a user's per-host value, so the fix lives in two layers.

- setup-lan-access.sh: always render the writable ~/.ssh-local/config sidecar
  (Host * ControlPath redirect into ~/.ssh-local/cm + Include ~/.ssh/config) on
  EVERY host OS. Previously the script exited early (no-op) on native Linux,
  leaving dssh/dscp broken when ~/.ssh was read-only there too. The host-jump
  block, its key generation, and the authorize hints stay gated on VM-backed
  detection / DEVBOX_LAN_ACCESS=jump (new NEED_JUMP flag).
- Dockerfile.base: document that the /etc/ssh drop-in default cannot override a
  user per-host ControlPath; cross-ref the two handling layers.
- entrypoint-user.sh: correct the now-stale "no-op on native Linux" comment.
- README.md / DOCKER_HUB.md: document read-only-~/.ssh ControlPath handling.

CHANGELOG: v1.1.5 (Fixed + Changed + pi 0.79.6 -> 0.79.7 auto-resolved bump).

entrypoint-user.sh

@@ -12,12 +12,16 @@ set -euo pipefail
 mkdir -p /tmp/sshcm
 chmod 700 /tmp/sshcm
 
-# ── LAN access: generic host-OS-agnostic reachability helper ────────
-# On VM-backed hosts (macOS OrbStack / Docker Desktop) the container can't
-# reach the host's directly-attached LAN peers by default; this generates a
-# writable ~/.ssh-local/config that uses the host as an SSH jump. On native
-# Linux (LAN reachable directly) it is a no-op. Controlled by DEVBOX_LAN_ACCESS
-# (auto|jump|off) + HOST_SSH_USER. Always non-fatal. See the script header.
+# ── LAN access + writable SSH sidecar: host-OS-agnostic helper ──────
+# Generates the writable ~/.ssh-local/config on EVERY host OS: a `Host *`
+# ControlPath redirect into ~/.ssh-local/cm (so `ssh -F` / dssh / dscp work
+# even when ~/.ssh is bind-mounted read-only) plus `Include ~/.ssh/config`. On
+# VM-backed hosts (macOS OrbStack / Docker Desktop) it ALSO adds an
+# SSH-jump-via-host block so the container can reach the host's
+# directly-attached LAN peers; on native Linux (LAN reachable directly) the
+# jump block is omitted but the sidecar is still rendered. Controlled by
+# DEVBOX_LAN_ACCESS (auto|jump|off) + HOST_SSH_USER. Always non-fatal. See the
+# script header.
 if [ -r /usr/local/lib/pi-devbox/setup-lan-access.sh ]; then
   bash /usr/local/lib/pi-devbox/setup-lan-access.sh || true
 fi