feat: add AgentMail (QQ) agent_qq provider

[Fromsko]

Summary

Request to add a provider for Tencent Agent Mail (https://agent.qq.com).

Agent Mail gives AI agents a dedicated @agent.qq.com email address. Public REST API base URL: https://api.agent.qq.com/v1.

Proposed actions

Action	Method	Path
list_aliases	GET	/v1/me
list_messages	GET	/v1/aliases/{alias_id}/messages
read_message	GET	/v1/aliases/{alias_id}/messages/{message_id}
send_message	POST	/v1/aliases/{alias_id}/messages/send
delete_message	DELETE	/v1/aliases/{alias_id}/messages/{message_id}

Authentication

Agent Mail uses OAuth access tokens (Authorization: Bearer <token>). Users can obtain one by running the official agently-cli auth login or completing the OAuth device flow.

Implementation PR: #180

[coderabbitai]

🔗 Related PRs

#64 - feat(provider): add qq_mail [merged]
#84 - feat: netease_mail [merged]
#121 - feat(feishu): user-OAuth Feishu provider — docx + Bitable reads [merged]

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