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/keyset/keyset_default.go

@@ -0,0 +1,19 @@
+//go:build purego || !(amd64 || arm64)
+// +build purego !amd64,!arm64
+
+package keyset
+
+func Lookup(keyset []byte, key []byte) int {
+	if len(key) > 16 {
+		return len(keyset) / 16
+	}
+	var padded [16]byte
+	copy(padded[:], key)
+
+	for i := 0; i < len(keyset); i += 16 {
+		if string(padded[:]) == string(keyset[i:i+16]) {
+			return i / 16
+		}
+	}
+	return len(keyset) / 16
+}