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_amd64.go

@@ -0,0 +1,13 @@
+// Code generated by command: go run equal_fold_asm.go -pkg ascii -out ../ascii/equal_fold_amd64.s -stubs ../ascii/equal_fold_amd64.go. DO NOT EDIT.
+
+//go:build !purego
+// +build !purego
+
+package ascii
+
+// EqualFoldString is a version of strings.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 EqualFoldString(a string, b string) bool