docs(runtime): outline mobile Feishu control contract

[axobase001]

Summary

Adds a docs-only design note for a future mobile / Feishu runtime control contract.

This is intentionally non-behavioral:

• no runtime code changes
• no new endpoints
• no mobile UI
• no Feishu bridge implementation

The document outlines:

• goals and non-goals
• local-first transport boundaries
• optional token/auth boundary expectations
• core thread/turn/event/approval resources
• minimal command surface
• event contract expectations
• approval semantics
• Feishu/Lark bridge notes
• suggested smaller PR slices

This is meant to align the larger remote-control direction with the smaller Feishu/Lark-first lane discussed in #757/#758 and the larger prototype in #852.

Verification

• git diff --check
• docs-only secret scan for common token patterns

[gemini-code-assist]

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[Hmbown]

thank you so much!!!

[Hmbown]

Thanks for writing this up. I am closing this PR because mobile/Feishu runtime planning is not admitted as public docs for the current release lane. Please keep this direction in the linked issue discussion until maintainer-approved implementation slices are ready; then open one small PR per accepted issue with a concrete verification plan.