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/golang.org/x/oauth2/transport.go

@@ -0,0 +1,75 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package oauth2
+
+import (
+	"errors"
+	"log"
+	"net/http"
+	"sync"
+)
+
+// Transport is an [http.RoundTripper] that makes OAuth 2.0 HTTP requests,
+// wrapping a base [http.RoundTripper] and adding an Authorization header
+// with a token from the supplied [TokenSource].
+//
+// Transport is a low-level mechanism. Most code will use the
+// higher-level [Config.Client] method instead.
+type Transport struct {
+	// Source supplies the token to add to outgoing requests'
+	// Authorization headers.
+	Source TokenSource
+
+	// Base is the base RoundTripper used to make HTTP requests.
+	// If nil, http.DefaultTransport is used.
+	Base http.RoundTripper
+}
+
+// RoundTrip authorizes and authenticates the request with an
+// access token from Transport's Source.
+func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
+	reqBodyClosed := false
+	if req.Body != nil {
+		defer func() {
+			if !reqBodyClosed {
+				req.Body.Close()
+			}
+		}()
+	}
+
+	if t.Source == nil {
+		return nil, errors.New("oauth2: Transport's Source is nil")
+	}
+	token, err := t.Source.Token()
+	if err != nil {
+		return nil, err
+	}
+
+	req2 := req.Clone(req.Context())
+	token.SetAuthHeader(req2)
+
+	// req.Body is assumed to be closed by the base RoundTripper.
+	reqBodyClosed = true
+	return t.base().RoundTrip(req2)
+}
+
+var cancelOnce sync.Once
+
+// CancelRequest does nothing. It used to be a legacy cancellation mechanism
+// but now only logs on first use to warn that it's deprecated.
+//
+// Deprecated: use contexts for cancellation instead.
+func (t *Transport) CancelRequest(req *http.Request) {
+	cancelOnce.Do(func() {
+		log.Printf("deprecated: golang.org/x/oauth2: Transport.CancelRequest no longer does anything; use contexts")
+	})
+}
+
+func (t *Transport) base() http.RoundTripper {
+	if t.Base != nil {
+		return t.Base
+	}
+	return http.DefaultTransport
+}