feat: add MCP endpoint exposing calendar tools over Streamable HTTP

Adds a POST /mcp endpoint (github.com/modelcontextprotocol/go-sdk) with
three tools mirroring the existing /calendar logic: get_calendar_today,
get_calendar_for_date and get_holidays. Bumps go.mod to Go 1.25 (required
by the SDK) and vendors the new dependencies. Also fixes an unanchored
.gitignore rule ("domogeek") that was silently excluding all untracked
files under cmd/domogeek/.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Hu8wwahgecuCGfesTKCfEd

vendor/github.com/segmentio/asm/internal/unsafebytes/unsafebytes.go

@@ -0,0 +1,20 @@
+package unsafebytes
+
+import "unsafe"
+
+func Pointer(b []byte) *byte {
+	return *(**byte)(unsafe.Pointer(&b))
+}
+
+func String(b []byte) string {
+	return *(*string)(unsafe.Pointer(&b))
+}
+
+func BytesOf(s string) []byte {
+	return *(*[]byte)(unsafe.Pointer(&sliceHeader{str: s, cap: len(s)}))
+}
+
+type sliceHeader struct {
+	str string
+	cap int
+}