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.

.gitignore

@@ -26,5 +26,10 @@ htmlcov/
 # build artifact from scripts/build-skill.sh
 /dist/
 
+# Go MCP bundle build outputs - source of truth for vendored/ stays under
+# skills/last30days/scripts/; build/ holds cross-compiled binaries + .mcpb files.
+/mcp/vendored/
+/mcp/build/
+
 # Internal planning docs (ce:plan output) — keep local, don't publish
 docs/plans/

mcp/.gitignore

@@ -0,0 +1,9 @@
+# Mirror of skills/last30days/scripts/, populated by scripts/sync-engine.sh.
+# Source of truth lives in the Python skill; never commit the mirror.
+vendored/
+
+# Local build output: cross-compiled binaries and packaged .mcpb files.
+build/
+# Anchor to the mcp/ root so the cmd/last30days-pp-mcp/ package directory
+# is not also excluded (subdirs with the same name would otherwise match).
+/last30days-pp-mcp

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.

mcp/cmd/last30days-pp-mcp/main.go

@@ -0,0 +1,11 @@
+// Package main is the entry point for the last30days MCP server bundled
+// as a .mcpb for Claude Desktop. See mcp/README.md for build instructions.
+package main
+
+// Version is stamped at build time via -ldflags "-X main.Version=<tag>".
+// Defaults to "dev" for local builds.
+var Version = "dev"
+
+func main() {
+	// Wired in U3.
+}

mcp/go.mod

@@ -0,0 +1,3 @@
+module github.com/mvanhorn/last30days-skill/mcp
+
+go 1.22

mcp/scripts/sync-engine.sh

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+# Mirrors skills/last30days/scripts/{last30days.py,lib/} into mcp/vendored/
+# so the Go binary's embed.FS captures the engine at build time.
+#
+# Source of truth: skills/last30days/scripts/. Never edit mcp/vendored/ directly.
+# Run before `go build` locally and in CI before `printing-press bundle`.
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+MCP_DIR="$(cd "${SCRIPT_DIR}/.." && pwd)"
+REPO_ROOT="$(cd "${MCP_DIR}/.." && pwd)"
+ENGINE_SRC="${REPO_ROOT}/skills/last30days/scripts"
+VENDORED="${MCP_DIR}/vendored"
+
+if [ ! -f "${ENGINE_SRC}/last30days.py" ]; then
+  echo "sync-engine: ${ENGINE_SRC}/last30days.py not found" >&2
+  exit 1
+fi
+
+rm -rf "${VENDORED}"
+mkdir -p "${VENDORED}"
+
+# Copy the entry script and the lib/ tree (modules + lib/vendor/).
+cp "${ENGINE_SRC}/last30days.py" "${VENDORED}/last30days.py"
+cp -R "${ENGINE_SRC}/lib" "${VENDORED}/lib"
+
+# Strip caches so the embed.FS stays deterministic.
+find "${VENDORED}" -type d -name "__pycache__" -prune -exec rm -rf {} +
+find "${VENDORED}" -type f -name "*.pyc" -delete
+
+echo "sync-engine: vendored engine at ${VENDORED}"