feat(simulator): add PDF export per offer and calculation explanations

- Add "Export PDF" button on each offer with detailed calculations
- Add collapsible "Comprendre les calculs" section explaining:
  - Subscription calculation (monthly × 12)
  - Energy cost breakdown by tariff type (BASE, HC/HP, TEMPO, SEASONAL, ZEN_FLEX)
  - Final total summary
- Fix isOffpeakHour function to handle {ranges: [...]} format from PDL config
- Tone down flashy gradient headers to muted gray style for better UX

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: Clément VALENTIN