pitch-deck: light mode support + MilestonesSlide redesign

- ArchitectureSlide: full light mode via useIsLight() hook, all inline styles adapt
- USPSlide: full light mode via useIsLight() hook, all inline styles adapt
- MilestonesSlide: new component — horizontal timeline with past/HEUTE/future,
  THEMES object (dark + light), clickable milestone nodes and stat cards with
  detail modal, bilingual (de/en), scaling via ResizeObserver
- PitchDeck: register new 'milestones' slide case

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pitch-deck/components/PitchDeck.tsx

@@ -52,6 +52,7 @@ import StrategySlide from './slides/StrategySlide'
 import FinanzplanSlide from './slides/FinanzplanSlide'
 import GlossarySlide from './slides/GlossarySlide'
 import RiskSlide from './slides/RiskSlide'
+import MilestonesSlide from './slides/MilestonesSlide'
 
 interface PitchDeckProps {
   lang: Language
@@ -182,6 +183,8 @@ export default function PitchDeck({ lang, onToggleLanguage, investor, onLogout,
         return <BusinessModelSlide lang={lang} products={data.products} investorId={investor?.id || null} preferredScenarioId={preferredScenarioId} isWandeldarlehen={isWandeldarlehen} />
       case 'traction':
         return <TractionSlide lang={lang} milestones={data.milestones} metrics={data.metrics} />
+      case 'milestones':
+        return <MilestonesSlide lang={lang} />
       case 'competition':
         return <CompetitionSlide lang={lang} features={data.features} competitors={data.competitors} />
       case 'team':