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

README.md

@@ -6,3 +6,9 @@ Tools for domotic
 
 Return calendar informations about today
 
+## MCP
+
+An MCP server is exposed over Streamable HTTP at `/mcp`, providing the same calendar
+information as MCP tools (`get_calendar_today`, `get_calendar_for_date`, `get_holidays`)
+for use by LLM agents/MCP clients.
+