fix(pitch-deck): fix Liquidität engine label mismatches + MilestonesSlide types

Engine now uses dynamic row_type-based summation instead of hardcoded label
strings that differed between scenarios (e.g. 'Summe ERTRÄGE' vs
'Summe EINZAHLUNGEN'), fixing stale 9.2M value in Wandeldarlehen scenarios.
Rolling balance now includes all financing cash flows via ÜBERSCHUSS chain.

MilestonesSlide: widen Theme type to union so t.key comparisons compile.

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

pitch-deck/components/slides/MilestonesSlide.tsx

@@ -147,7 +147,7 @@ const THEMES = {
   },
 }
 
-type Theme = typeof THEMES.dark
+type Theme = typeof THEMES.dark | typeof THEMES.light
 
 // ── Data ──────────────────────────────────────────────────────────────────────
 const TODAY_POSITION = 0.56