feat: allow excluding built-in tools from agent sandbox

[Opaius]

Problem

Flue's createAgent() and the sandbox createBuiltinTools provide built-in tools (read, edit, bash, grep, glob, task). No public API to opt out of specific ones. Only workaround is hijacking the internal createBuiltinTools prototype:

const original = proto.createBuiltinTools;
proto.createBuiltinTools = function (...args) {
  return original.apply(this, args).filter((t) => t.name !== 'task');
};

Fragile — depends on internal API naming.

Requested

excludeTools?: string[] on agent runtime config or sandbox options.

Use case

Apps with custom tool orchestration don't want the AI seeing Flue's default task tool — adds redundant/confusing LLM options.

v0.9.2