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/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}"