Add MCP server: expose memwalk as tools for Claude Code / opencode / agents

New `memwalk mcp` subcommand starts a stdio MCP server exposing four
tools: ask, standup, status, update. The underlying memba Session is
loaded lazily on the first call that needs the model, then reused for
the lifetime of the process — first query ~2s, subsequent <500ms.

- memwalk/mcp_server.py — Server + tool list/dispatch using mcp SDK
- memwalk/cli.py        — `memwalk mcp` subcommand wires it up
- pyproject.toml        — mcp>=1.0.0 dependency
- README.md             — setup instructions for Claude Code and opencode

Verified locally: tools/list returns all 4, tools/call status returns
the expected JSON without loading the model.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

README.md

@@ -53,6 +53,55 @@ saved to `~/.memwalk/current.memb` via memba.
 `memwalk ask` and `memwalk standup` load that state and query it.  The model
 recalls themes, projects, and trajectory across processes and reboots.
 
+## Use from an agent (MCP)
+
+memwalk ships an MCP server so Claude Code / opencode / any MCP-aware
+agent can query your memory as native tools.
+
+```bash
+memwalk mcp     # starts a stdio MCP server
+```
+
+Tools exposed: `ask(question)`, `standup()`, `status()`, `update()`.
+The Session loads lazily on the first call that needs it, then stays in
+memory — first call ~2 s, subsequent calls <500 ms.
+
+### Configure Claude Code
+
+Easiest way (Claude Code CLI):
+
+```bash
+claude mcp add memwalk -- memwalk mcp
+```
+
+Or by hand, in `~/.claude/mcp_servers.json` (path may vary by version):
+
+```json
+{
+  "mcpServers": {
+    "memwalk": {
+      "command": "memwalk",
+      "args": ["mcp"]
+    }
+  }
+}
+```
+
+Restart Claude Code. Tools appear as `mcp__memwalk__ask`,
+`mcp__memwalk__standup`, etc.
+
+### Configure opencode
+
+opencode uses its own MCP block in `opencode.json`:
+
+```json
+{
+  "mcpServers": {
+    "memwalk": { "command": "memwalk", "args": ["mcp"] }
+  }
+}
+```
+
 ## Layout
 
 ```