Enhance agent features and CLI with testing improvements

[alDuncanson]

This pull request introduces comprehensive agent-oriented documentation and skill packs to support development, testing, and release workflows for the handler project. It also adds a scheduled and manual smoke test automation for the Pilotty TUI using CI and local scripts. The most important changes are grouped below:

Agent Documentation and Skill Packs

• Added agent documentation in docs/agent, including the agent DX contract (agent-dx-contract.md), context playbook (CONTEXT.md), and a directory README outlining their purpose. These documents define compatibility guarantees, safe execution patterns, and repository-local skills for agents. [1] [2] [3]
• Introduced local skill packs in .agents/skills for development (developing-handler), testing (testing-handler), and releasing (releasing-handler). Each skill includes a detailed workflow, guardrails, and done criteria for agent-driven operations. [1] [2] [3] [4]

Pilotty TUI Smoke Test Automation

• Added a CI workflow (.github/workflows/pilotty-smoke.yml) to run scheduled and manual Pilotty TUI smoke tests, ensuring agent-style TUI automation checks are performed regularly.
• Updated README.md to document Pilotty TUI smoke automation, including installation instructions and usage of the just pilotty-smoke command.

A2A Protocol Specification

• Added initial protocol specification files under docs/spec/a2a, including the preface, introduction, and terminology sections. These files describe the protocol's goals, structure, and key concepts for agent interoperability. [1] [2] [3]

These changes collectively provide a foundation for agent-driven development, testing, release, and protocol reference, improving both human and machine-facing workflows.