feat(ai): add openspec integration

[nashtsai]

Summary

This PR adds OpenSpec integration to KubeBlocks, providing structured change management capabilities for AI-assisted development.

Changes

• Add OpenSpec commands for change lifecycle management (/opsx-*)
• Add AGENTS.md hierarchical documentation system
• Provide structured skill definitions for AI operations
• Support change exploration, creation, verification, and archival

Files Added

• .claude/commands/opsx/* - Claude Code command definitions
• .claude/skills/openspec-*/SKILL.md - Claude skill implementations
• .opencode/command/opsx-* - OpenCode command definitions
• .opencode/skills/openspec-*/SKILL.md - OpenCode skill implementations
• openspec/config.yaml - OpenSpec configuration
• AGENTS.md (root + subdirs) - Hierarchical project documentation

Review / Merge checklist

• PR title and summary are descriptive
• Docs updated (AGENTS.md provides project documentation)
• Tests included (if applicable)

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