Add MemPalace local-first AI memory system to base image

Install mempalace via pip in the Dockerfile. Provides 29 MCP tools
for semantic search over conversation history, knowledge graph
queries, agent diaries, and wing/room/drawer management. Everything
runs locally — no API keys, no data egress.

Integration:
- Dockerfile: pip install mempalace (with --break-system-packages
  for Debian trixie PEP 668 compliance)
- entrypoint-user.sh: auto-initializes palace for /workspace on
  first run (idempotent, skips if palace exists)
- entrypoint.sh: adds ~/.mempalace to the volume ownership-fix loop
- docker-compose.yml + shared: optional devbox-palace named volume
  at ~/.mempalace (commented out by default — user opts in)

Users configure MCP integration by adding a mempalace server entry
to their opencode.json. No wrapper plugin needed — the upstream
Python MCP server is used directly.

Docs updated: README.md (new MemPalace section with setup, MCP
config, usage examples, storage details), DOCKER_HUB.md (data
storage table + tools list), CHANGELOG.md (unreleased entry).

README.md

@@ -444,6 +444,61 @@ The `--use-device-code` flag outputs a URL and short code instead of trying to o
 
 SSO sessions typically last 8–12 hours before requiring re-authentication. Since `~/.aws` is mounted from the host, tokens persist across container restarts.
 
+## MemPalace — persistent AI memory
+
+The image includes [MemPalace](https://github.com/MemPalace/mempalace), a local-first AI memory system that stores conversation history verbatim and retrieves it via semantic search. Nothing leaves your machine.
+
+### Enabling persistence
+
+Uncomment the palace volume in `docker-compose.yml`:
+
+```yaml
+- devbox-palace:/home/developer/.mempalace
+```
+
+Without the volume, palace data lives in the container's writable layer and is lost on `--force-recreate`.
+
+### MCP integration with opencode
+
+Add mempalace as an MCP server in your `opencode.json` (inside `~/.config/opencode/`):
+
+```json
+{
+  "mcp": {
+    "mempalace": {
+      "type": "local",
+      "command": ["python3", "-m", "mempalace.mcp_server"]
+    }
+  }
+}
+```
+
+This gives opencode access to 29 MCP tools for searching memory, querying the knowledge graph, managing wings/rooms/drawers, and agent diaries.
+
+### Basic usage
+
+```bash
+# Mine project files into the palace
+mempalace mine /workspace
+
+# Mine conversation transcripts
+mempalace mine ~/.local/share/opencode/ --mode convos
+
+# Search memory
+mempalace search "why did we switch to eno1"
+
+# Load context for a new session
+mempalace wake-up
+```
+
+Each workspace gets its own isolated "wing" — memories never leak between projects.
+
+### Storage
+
+- **Palace data** (ChromaDB vectors, SQLite knowledge graph, drawers): `~/.mempalace/` — persists via the `devbox-palace` named volume
+- **Embedding model** (~300 MB): downloaded on first use, cached inside the palace directory
+- **No API keys required** for core functionality (local embeddings via ONNX)
+
 ## Shell defaults
 
 The image ships a baked `.bash_aliases` and `.inputrc` with quality-of-life defaults. On first container start they are copied from `/etc/skel-devbox/` into `/home/developer/` **only if the target file does not already exist** — so host bind-mounts and any version you've customized inside the container are never overwritten on upgrade.