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/encoding/json/reflect_optimize.go

@@ -0,0 +1,30 @@
+//go:build !go1.20
+// +build !go1.20
+
+package json
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+//go:linkname unsafe_NewArray reflect.unsafe_NewArray
+func unsafe_NewArray(rtype unsafe.Pointer, length int) unsafe.Pointer
+
+//go:linkname typedslicecopy reflect.typedslicecopy
+//go:noescape
+func typedslicecopy(elemType unsafe.Pointer, dst, src slice) int
+
+func extendSlice(t reflect.Type, s *slice, n int) slice {
+	elemTypeRef := t.Elem()
+	elemTypePtr := ((*iface)(unsafe.Pointer(&elemTypeRef))).ptr
+
+	d := slice{
+		data: unsafe_NewArray(elemTypePtr, n),
+		len:  s.len,
+		cap:  n,
+	}
+
+	typedslicecopy(elemTypePtr, d, *s)
+	return d
+}