Bake mempalace-toolkit wrappers into the image

The scheduler templates in mempalace-toolkit's contrib/ assume
mempalace-session is available inside the container, but the image
never actually installed it. Users following the *-devbox scheduler
docs would silently lose the wrappers on every container recreate,
because the only way to get them was a post-hoc install.sh inside
the container — which lives in the ephemeral layer. The host-side
systemd timer would then fire, docker exec in, and hit
"mempalace-session: command not found".

Caught during runtime validation on 2026-04-30: host-side systemd
unit ran cleanly at 16:15 today, then the container was rebuilt
and recreated, and the wrappers were gone. The rebuild produced
an image that the scheduler template's own documented precondition
did not hold for.

Fix: new Dockerfile block clones mempalace-toolkit at build time
(depth-1) to /opt/mempalace-toolkit/, symlinks bin/mempalace-session
and bin/mempalace-docs into /usr/local/bin/, asserts both respond
to --help before the layer succeeds. Gated by
INSTALL_MEMPALACE_TOOLKIT=true (defaults on, depends on
INSTALL_MEMPALACE=true). Floated ref via MEMPALACE_TOOLKIT_REF=main
for auto-picking-up toolkit updates; override for reproducible
builds once the toolkit starts tagging releases.

Smoke test gains three assertions (mempalace-session --help,
mempalace-docs --help, symlink target check). Resolved-versions
preamble logs the toolkit git short-SHA alongside the other
floated components, so CI logs always record what got baked in.

README gains a Scheduled mining (mempalace-toolkit) subsection
and a build-args row. DOCKER_HUB.md regenerated; sync-check passes.

Dockerfile

@@ -207,6 +207,31 @@ RUN if [ "${INSTALL_MEMPALACE}" = "true" ]; then \
       /opt/uv-tools/mempalace/bin/python -c "import mempalace; print('mempalace', mempalace.__version__ if hasattr(mempalace, '__version__') else 'installed')" ; \
     fi
 
+# ── mempalace-toolkit — bash wrappers for session/docs mining ────────
+# Thin wrappers (`mempalace-session`, `mempalace-docs`) that delegate to
+# the mempalace Python CLI for two common scheduled tasks:
+#   - mempalace-session: mines opencode's SQLite session history into
+#     the palace (wing_conversations). Referenced by contrib/ scheduler
+#     templates (systemd user timer, cron) in the toolkit repo.
+#   - mempalace-docs: mines project docs into a per-project wing.
+# Repo source of truth: https://gitea.jordbo.se/joakimp/mempalace-toolkit
+#
+# Requires INSTALL_MEMPALACE=true (wrappers shell out to `mempalace`).
+# Disable with --build-arg INSTALL_MEMPALACE_TOOLKIT=false if you don't
+# use the scheduled-mining workflow.
+ARG INSTALL_MEMPALACE_TOOLKIT=true
+ARG MEMPALACE_TOOLKIT_REF=main
+RUN if [ "${INSTALL_MEMPALACE}" = "true" ] && [ "${INSTALL_MEMPALACE_TOOLKIT}" = "true" ]; then \
+      git clone --depth 1 --branch "${MEMPALACE_TOOLKIT_REF}" \
+        https://gitea.jordbo.se/joakimp/mempalace-toolkit.git /opt/mempalace-toolkit && \
+      ln -sf /opt/mempalace-toolkit/bin/mempalace-session /usr/local/bin/mempalace-session && \
+      ln -sf /opt/mempalace-toolkit/bin/mempalace-docs    /usr/local/bin/mempalace-docs && \
+      chmod +x /opt/mempalace-toolkit/bin/mempalace-session /opt/mempalace-toolkit/bin/mempalace-docs && \
+      mempalace-session --help >/dev/null && \
+      mempalace-docs    --help >/dev/null && \
+      echo "mempalace-toolkit installed at $(cd /opt/mempalace-toolkit && git rev-parse --short HEAD)" ; \
+    fi
+
 # rustup — Rust toolchain manager
 # Installs the rustup-init binary only. Users bootstrap Rust with:
 #   rustup-init -y && source ~/.cargo/env