LAN-access: fix Include scope + read-only ControlPath, add ssh-lan.conf & RFC1918 autojump

- Fix: Include ~/.ssh/config was scoped to the Host host/mac block, so
  dssh <peer> by name fell back to SSH defaults. Emit Host * scope reset
  before every Include.
- Fix: redirect ControlPath to writable ~/.ssh-local sidecar (Mac config's
  ~/.ssh/cm path is read-only in the container, broke multiplexed hosts).
- Add: Include host-owned ~/.config/devbox-shell/ssh-lan.conf for named-peer
  ProxyJump overrides (keeps image generic; peer names stay host-side).
- Add: opt-in DEVBOX_LAN_AUTOJUMP_PRIVATE=1 RFC1918 catch-all for roaming.
- Docs: README/.env.example/AGENTS/CHANGELOG + new ssh-lan.conf.example.

ssh-lan.conf.example

@@ -0,0 +1,45 @@
+# ssh-lan.conf.example — host-owned LAN-peer jump overrides for opencode-devbox
+# ============================================================================
+# WHAT THIS IS
+#   On a VM-backed host (macOS OrbStack / Docker Desktop) the container can't
+#   reach the host's LAN directly; it tunnels through the host via the `host`
+#   SSH jump that the entrypoint sets up (see the README "Reaching your LAN"
+#   section). To reach your LAN peers *by name*, they need `ProxyJump host`.
+#
+# WHY NOT JUST EDIT ~/.ssh/config?
+#   The host itself reaches those peers DIRECTLY — adding `ProxyJump host`
+#   there would break the host's own access (and ~/.ssh is mounted read-only
+#   into the container anyway). So container-only jump overrides live HERE.
+#
+# HOW IT'S WIRED
+#   If this file exists at  ~/.config/devbox-shell/ssh-lan.conf  on the host
+#   (the same bind-mounted devbox-shell bridge dir used for shared aliases),
+#   the generated ~/.ssh-local/config Includes it BEFORE your ~/.ssh/config.
+#   SSH's first-value-wins rule means ProxyJump is taken from here, while
+#   HostName / User / IdentityFile are inherited from the matching block in
+#   your ~/.ssh/config. So you only list the names + the jump — nothing else.
+#
+# SETUP
+#   1. Copy to your host:  cp ssh-lan.conf.example ~/.config/devbox-shell/ssh-lan.conf
+#   2. Bind-mount ~/.config/devbox-shell into the container (most setups
+#      already do this for shared shell aliases).
+#   3. List the host aliases (as named in your ~/.ssh/config) that should be
+#      reached through the host jump.
+#   4. Restart the container, then:  dssh <name>
+#
+# NOTE: these are facts about ONE host's LAN. A roaming laptop sees different
+# networks — keep this per-host, never in the image. For ad-hoc private IPs on
+# whatever LAN you're currently on, prefer DEVBOX_LAN_AUTOJUMP_PRIVATE=1
+# instead of naming every peer.
+
+# Example — names must match Host blocks already defined in your ~/.ssh/config:
+Host pve pve-2 pbs-vm my-nas
+    ProxyJump host
+
+# You can also give a peer its own settings here if it isn't in ~/.ssh/config
+# at all (then specify everything, not just ProxyJump):
+# Host lab-box
+#     HostName 192.168.1.77
+#     User admin
+#     IdentityFile ~/.ssh/id_ed25519
+#     ProxyJump host