feat: add ENABLE_CLAUDEAI_MCP_SERVERS opt-out setting

Adds a toggle in the MCP Servers settings section to control whether
Claude Code connects to MCP servers configured in Claude.ai. When
disabled, sets ENABLE_CLAUDEAI_MCP_SERVERS=false. Also fixes a
pre-existing omission of disable_cron from the TypeScript HikariConfig
interface.

Closes #210

src/lib/commands/slashCommands.test.ts

@@ -66,6 +66,7 @@ vi.mock("$lib/stores/config", () => ({
       disable_1m_context: false,
       max_output_tokens: null,
       include_git_instructions: true,
+      enable_claudeai_mcp_servers: true,
     }),
   },
 }));