docs: build a local agent example with llamadart

[leehack]

Feature Description

Build a local agent example showing llamadart calling MCP tools through mcp_dart.

Motivation

A local GGUF-powered agent demonstrates a strong combined-project story for Dart AI apps and MCP tooling.

Proposed Solution

Show:

• local GGUF model calls MCP tools via mcp_dart
• structured tool calls
• tool result injection
• Flutter UI
• cross-linking to llamadart work if this becomes cross-repo

Acceptance Criteria

• The example has clear setup instructions and model/file assumptions.
• Tool-call flow is documented end-to-end.
• Cross-repo dependencies are pinned or clearly explained.