Add Claude Code agents and CLAUDE.md

[TsekNet]

Add project conventions and 2 specialized review agents:

• CLAUDE.md: project conventions, build commands, package layout, agent routing
• .claude/agents/diff-reviewer.md: semantic diff engine, match keys, parser safety
• .claude/agents/output-reviewer.md: terminal/JSON/markdown renderer correctness

[TsekNet]

Merged via #35