chore: adopt Ecosystem Interaction Protocol in GEMINI.md and CLAUDE.md

[MrBT-nano]

Proposal: Adopt Ecosystem Interaction Protocol for AI Agents

To ensure safe and coordinated development across the vtuber-* ecosystem, we propose adding an Ecosystem Interaction Protocol to this repository's GEMINI.md and CLAUDE.md files.

This protocol has already been adopted by vtuber-commons to prevent AI agents from making uncoordinated cross-repo changes.

Proposed Addition

Please add the following section to both GEMINI.md and CLAUDE.md (usually under or after the "Automated Lifecycle Management" section):

## 🌐 Ecosystem Interaction Protocol
1. **Multi-Repo Boundaries:** You MUST NOT directly modify code in other `vtuber-*` repositories (especially `vtuber-contracts`).
2. **Issue-Based Communication:** When a change or resource is needed from another repository, you MUST:
   - Draft the requirements locally in `docs/specs/ecosystem/`.
   - Create a GitHub Issue in the target repository using `gh issue create`.
   - Reference the Issue URL in your local progress reports.
3. **Dependency Sync:** Only implement features depending on external changes (like new Schemas) after the corresponding Issue is resolved and released.

Benefits

• Safety: Prevents accidental or uncoordinated changes across repositories.
• Traceability: Ensures all cross-repo dependencies are documented via GitHub Issues.
• Human-in-the-loop: Requires human review of the issues before agents proceed with dependent work.