Validate each configured target file independently

[erkininfinity]

Goal

Make agentready-kit check report completeness for each generated target independently, not only through the aggregate score.

Suggested scope

• Keep the current aggregate AgentReady Score.
• Add a per-target pass/fail summary for AGENTS.md, CLAUDE.md, Copilot instructions, and Cursor rules.
• Add tests that fail when one target is missing required sections.

Why this helps

A repository can look ready overall while one target file is incomplete. Per-target validation makes the report more actionable.