feat(mcp): scaffold Go module under mcp/ for Claude Desktop bundle

Add a new top-level mcp/ Go module that will host the Claude Desktop MCPB
server. U1 of the Claude Desktop .mcpb bundle plan: scaffold only, no
behavior yet.

- mcp/go.mod targets Go 1.22+ with mark3labs/mcp-go as the planned
  dependency (added in U3 when the server wiring lands).
- mcp/scripts/sync-engine.sh mirrors skills/last30days/scripts/ into
  mcp/vendored/ before each build, keeping the Code skill and Desktop
  bundle on the same engine source.
- Root .gitignore excludes mcp/vendored/ and mcp/build/ so the engine
  mirror and cross-compiled binaries stay local.

mcp/README.md

@@ -0,0 +1,36 @@
+# last30days-pp-mcp
+
+Go MCP server that wraps the last30days Python engine for Claude Desktop. Packaged as a `.mcpb` bundle (drag-drop install into Claude Desktop).
+
+The MCP server exposes a single `research` tool that mirrors the `/last30days <topic>` slash command available in Claude Code. At runtime the binary extracts the vendored Python engine into a per-user cache and shells out to `python3` to produce the synthesis input Claude renders.
+
+## Architecture
+
+- `cmd/last30days-pp-mcp/` - server entry point
+- `internal/engine/` - `embed.FS` of the Python engine + cache extractor + subprocess wrapper
+- `internal/tools/` - MCP tool handlers (currently `research`)
+- `vendored/` - mirror of `skills/last30days/scripts/`, generated by `scripts/sync-engine.sh` (gitignored)
+- `manifest.json` - MCPB v0.3 manifest consumed by Claude Desktop and `printing-press bundle`
+
+## Local build
+
+```bash
+# Mirror the Python engine into vendored/.
+bash scripts/sync-engine.sh
+
+# Build for the current host.
+go build -ldflags "-X main.Version=dev" -o build/last30days-pp-mcp ./cmd/last30days-pp-mcp
+
+# Package as a .mcpb (requires the printing-press binary on PATH).
+printing-press bundle . --skip-build --binary build/last30days-pp-mcp
+```
+
+The output `.mcpb` lands at `build/last30days-pp-mcp-<os>-<arch>.mcpb`. Drag it into Claude Desktop's Extensions panel to install.
+
+## Runtime requirements
+
+End users need Python 3.12+ on PATH. The bundle ships the engine source but relies on the host interpreter.
+
+## Versioning
+
+The MCPB `manifest.json` version is hand-bumped in the same PR that ships engine changes worth releasing. Release CI stamps the Go binary's `main.Version` from the tag.