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.

scripts/smoke-test.sh

@@ -99,7 +99,7 @@ echo "-- Optional / variant-gated --"
 # mempalace: present unless built with INSTALL_MEMPALACE=false
 if docker run --rm --entrypoint="" "$IMAGE" sh -c "command -v mempalace" >/dev/null 2>&1; then
   run "mempalace"             "mempalace --help | head -1"
-  run "mempalace-mcp-server"  "test -x /usr/local/bin/mempalace-mcp-server && echo wrapper-present"
+  run "mempalace-mcp"         "test -x /usr/local/bin/mempalace-mcp && readlink /usr/local/bin/mempalace-mcp"
 else
   echo "  - mempalace not installed (INSTALL_MEMPALACE=false)"
 fi