[P3] Refactor: extract a shared ScrollytellingWrapper, relocate shared utils, remove `any`

[dmchaledev]

Context

CODE-QUALITY-AUDIT.md §1 (Top-5 #3). The three scrollytelling components are 100% structurally identical (~47 lines each), differing only in name and which StickyVisualization/NarrativeSteps they import:

• src/components/eviction-data/EvictionScrollytelling.tsx
• src/components/campaign-finance-data/CampaignFinanceScrollytelling.tsx
• src/components/sidewalk-data/SidewalkScrollytelling.tsx

The work

• Extract a generic ScrollytellingWrapper taking the viz + steps as props/children; collapse the three files to thin wrappers.
• Move shared useLocale.ts and styles.css out of sidewalk-data/ (where eviction & campaign-finance currently reach across to import them) into src/components/shared/ or src/utils/.
• Replace the two let scroller: any declarations with the proper scrollama type already used in the sidewalk component.
• Adopt the configured path aliases (@components/*, etc.) consistently while touching these files.

Effort: Low (~an hour). Removes ~100 lines of duplication and the only any types in the codebase.

Priority: Low — code-health cleanup, no user-facing change.