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/sys/unix/sysvshm_unix.go

@@ -2,16 +2,11 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build (darwin && !ios) || linux
-// +build darwin,!ios linux
+//go:build (darwin && !ios) || linux || zos
 
 package unix
 
-import (
-	"unsafe"
-
-	"golang.org/x/sys/internal/unsafeheader"
-)
+import "unsafe"
 
 // SysvShmAttach attaches the Sysv shared memory segment associated with the
 // shared memory identifier id.
@@ -34,12 +29,7 @@ func SysvShmAttach(id int, addr uintptr, flag int) ([]byte, error) {
 	}
 
 	// Use unsafe to convert addr into a []byte.
-	// TODO: convert to unsafe.Slice once we can assume Go 1.17
-	var b []byte
-	hdr := (*unsafeheader.Slice)(unsafe.Pointer(&b))
-	hdr.Data = unsafe.Pointer(addr)
-	hdr.Cap = int(info.Segsz)
-	hdr.Len = int(info.Segsz)
+	b := unsafe.Slice((*byte)(unsafe.Pointer(addr)), int(info.Segsz))
 	return b, nil
 }