Update 20251212-ksef-business-model.md - Fix penalty timeline

[eoln]

Task

Fix penalty date in the KSeF business model research document.

Changes Required

• Fix penalty date at lines ~35, ~53 in timeline tables
• Add grace period explanation in section 1.3
• Update "KSeF Regulatory Timeline" table
• Add note about penalty-free 2026

File: .claude/research/20251212-ksef-business-model.md

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