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.

DOCKER_HUB.md

@@ -421,13 +421,13 @@ Add mempalace as an MCP server in your `opencode.json` (inside `~/.config/openco
   "mcp": {
     "mempalace": {
       "type": "local",
-      "command": ["mempalace-mcp-server"]
+      "command": ["mempalace-mcp"]
     }
   }
 }
 ```
 
-> The image installs mempalace into an isolated `uv tool` venv at `/opt/uv-tools/mempalace`. The `mempalace-mcp-server` wrapper on `PATH` exec's the venv's Python with the `mempalace.mcp_server` module — you don't need to know about the venv to use it.
+> The image installs mempalace into an isolated `uv tool` venv at `/opt/uv-tools/mempalace/`. `uv tool install` places `mempalace-mcp` on `PATH` as a shim whose shebang points at the venv's Python, so MCP clients can invoke it as a normal binary without worrying about the venv. Do **not** use `["python3", "-m", "mempalace.mcp_server"]` — the system Python cannot import from the uv-managed venv and you'll get `ModuleNotFoundError` / `MCP error -32000: connection closed`.
 
 This gives opencode access to 29 MCP tools for searching memory, querying the knowledge graph, managing wings/rooms/drawers, and agent diaries.