docs: align pace-aware quota documentation for beta

[rygel]

Summary

• update README and user manual with current pace-aware quota behavior
• document Pace-Aware Quota Colours, On pace badge, and used/raw behavior when disabled
• align provider detail contract with current window kinds and period-duration requirements
• add architecture notes for upstream period-duration enrichment and no downstream fallback lookups
• add concise Unreleased changelog entry for documentation updates

Scope

• documentation only
• no runtime code changes

[github-actions]

Build Performance Report

⏱️ Build Time: 12 minutes

📊 Comparison with main branch:

• Baseline (avg): 10 minutes
• Current: 12 minutes
• Change: 📈 20%

✅ Within acceptable range

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This is an automated performance check