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/ascii/equal_fold.go

@@ -0,0 +1,30 @@
+package ascii
+
+import (
+	"github.com/segmentio/asm/internal/unsafebytes"
+)
+
+// EqualFold is a version of bytes.EqualFold designed to work on ASCII input
+// instead of UTF-8.
+//
+// When the program has guarantees that the input is composed of ASCII
+// characters only, it allows for greater optimizations.
+func EqualFold(a, b []byte) bool {
+	return EqualFoldString(unsafebytes.String(a), unsafebytes.String(b))
+}
+
+func HasPrefixFold(s, prefix []byte) bool {
+	return len(s) >= len(prefix) && EqualFold(s[:len(prefix)], prefix)
+}
+
+func HasSuffixFold(s, suffix []byte) bool {
+	return len(s) >= len(suffix) && EqualFold(s[len(s)-len(suffix):], suffix)
+}
+
+func HasPrefixFoldString(s, prefix string) bool {
+	return len(s) >= len(prefix) && EqualFoldString(s[:len(prefix)], prefix)
+}
+
+func HasSuffixFoldString(s, suffix string) bool {
+	return len(s) >= len(suffix) && EqualFoldString(s[len(s)-len(suffix):], suffix)
+}