feat: host-agnostic LAN access (base) + fork/recall in pi variants

Item A — LAN access (base image):
- New rootfs/usr/local/lib/opencode-devbox/setup-lan-access.sh, invoked
  non-fatally from entrypoint-user.sh. On VM-backed hosts (macOS OrbStack /
  Docker Desktop, detected via host.docker.internal) it generates a writable
  ~/.ssh-local/config that uses the host as an SSH jump to reach LAN peers;
  no-op on native Linux. Ships the mechanism (generic 'host' jump alias),
  not policy (targets stay in the user's bind-mounted ~/.ssh/config).
- New env knobs: DEVBOX_LAN_ACCESS (auto|jump|off), HOST_SSH_USER,
  DEVBOX_HOST_ALIAS. dssh/dscp aliases in .bash_aliases (guarded).

Item B — pi-fork (fork) + pi-observational-memory (recall) in pi variants:
- Dockerfile.variant clones both elpapi42 repos to /opt and runs npm install
  there at build time (local-path 'pi install' does not npm-install, so deps
  must be present to load). New args PI_FORK_REPO/REF, PI_OBSMEM_REPO/REF.
- entrypoint-user.sh registers them at runtime via 'pi install /opt/<pkg>'
  (instant, in-place, idempotent; tools bind on next pi start).
- CI resolve-versions resolves each repo's master HEAD to a commit SHA and
  passes PI_FORK_REF/PI_OBSMEM_REF — same cache-hit guard as PI_VERSION.
- smoke-test asserts /opt clones + node_modules + settings.json registration;
  size thresholds bumped (with-pi 2700->2900, omos-with-pi 3700->3900).

Versions unchanged (opencode 1.15.13, pi 0.78.0 — both still latest).
Docs: README LAN section + env table, .env.example, AGENTS.md, CHANGELOG.
Plan recorded in docs/plan-lan-access-and-pi-extensions.md.

.env.example

@@ -31,6 +31,30 @@ WORKSPACE_PATH=~/projects
 # Path to SSH keys on host
 SSH_KEY_PATH=~/.ssh
 
+# ── LAN access from the container (host-OS-agnostic) ─────────────────
+# On VM-backed hosts (macOS OrbStack / Docker Desktop, also Docker Desktop
+# on Windows) the container runs in a Linux VM and CANNOT reach the host's
+# directly-attached LAN peers by default. On native Linux Docker the LAN is
+# reachable directly and nothing is needed. The entrypoint detects this and,
+# on VM-backed hosts, generates ~/.ssh-local/config so the host can be used
+# as an SSH jump (use the `dssh` alias, or add `ProxyJump host` to targets
+# in your bind-mounted ~/.ssh/config).
+#
+# DEVBOX_LAN_ACCESS: auto (default) | jump | off
+#   auto = set up the jump only on VM-backed hosts; no-op on native Linux.
+#   jump = always set up (e.g. native Linux with extra_hosts host-gateway).
+#   off  = disable entirely.
+# DEVBOX_LAN_ACCESS=auto
+#
+# HOST_SSH_USER: your username on the host. REQUIRED for the jump to
+# authenticate. On first start the entrypoint prints the public key to
+# authorize on the host (append to the host's ~/.ssh/authorized_keys) and
+# reminds you to enable the host's SSH server (e.g. macOS Remote Login).
+# HOST_SSH_USER=
+#
+# DEVBOX_HOST_ALIAS: host hostname to reach (default host.docker.internal).
+# DEVBOX_HOST_ALIAS=host.docker.internal
+
 # ── Skillset (agent skills and instructions) ─────────────────────────
 # If you have a skillset repo, the entrypoint auto-deploys skills and
 # instructions on container start using relative symlinks (portable