chore: sync shared ai prompts

[jan-kubica]

Summary

• add the shared ai-shared submodule and generated AGENTS/CLAUDE/GEMINI guidance
• add sync wrappers and an AI Instructions workflow that checks generated prompt drift
• add repo-specific local instructions for this package

Checks

• bash -n scripts/sync-ai-skills.sh scripts/link-codex-skills.sh
• bash scripts/sync-ai-skills.sh --check

[gemini-code-assist]

Code Review

This pull request integrates shared AI agent skills and guidelines into the repository by adding a .ai/shared submodule, setting up skill definitions under .agents/skills/ and .claude/commands/, and updating documentation files like AGENTS.md, CLAUDE.md, and GEMINI.md. It also introduces helper scripts link-codex-skills.sh and sync-ai-skills.sh. The review feedback correctly points out that these scripts assume execution from the repository root and recommends making them location-independent by dynamically resolving their paths.

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