Use mempalace-mcp entry point directly, drop redundant wrapper

The mempalace Python package ships a 'mempalace-mcp' console entry
point; 'uv tool install' places it on PATH as a shim whose shebang
points at the isolated venv's Python. Our hand-rolled wrapper at
/usr/local/bin/mempalace-mcp-server was duplicating what uv installs
for free — one less file to maintain.

Fixes the MCP error users saw after the v1.14.28b → v1.14.29 upgrade
path: custom opencode.json files typically had the pre-v1.14.29
command ['python3', '-m', 'mempalace.mcp_server'] which worked with
the old pip install but fails silently after the uv-tool migration
because system python3 cannot import from the venv. Opencode surfaced
this as 'MCP error -32000: connection closed'.

- generate-config.py now emits ['mempalace-mcp'] and keys its detect
  on shutil.which('mempalace-mcp').
- Dockerfile drops 'COPY rootfs/usr/local/bin/' and the chmod of the
  wrapper. Build shrinks from 30 to 29 stages.
- rootfs/usr/local/bin/ removed entirely.
- Smoke test asserts /usr/local/bin/mempalace-mcp is executable and
  prints its symlink target.
- README's MemPalace section shows ['mempalace-mcp'] and explicitly
  warns against the old pattern with the observed failure mode.
- CHANGELOG adds a v1.14.29c entry.

Dockerfile

@@ -340,11 +340,9 @@ COPY rootfs/home/developer/.inputrc      /etc/skel-devbox/.inputrc
 
 # ── Entrypoint ────────────────────────────────────────────────────────
 COPY rootfs/usr/local/lib/opencode-devbox/ /usr/local/lib/opencode-devbox/
-COPY rootfs/usr/local/bin/ /usr/local/bin/
 COPY entrypoint.sh /usr/local/bin/entrypoint.sh
 COPY entrypoint-user.sh /usr/local/bin/entrypoint-user.sh
 RUN chmod +x /usr/local/bin/entrypoint.sh /usr/local/bin/entrypoint-user.sh \
-    /usr/local/bin/mempalace-mcp-server \
     /usr/local/lib/opencode-devbox/*.py
 
 # Start as root — entrypoint adjusts UID/GID then drops to developer