fix: resolve structured data validation errors across app, tutorial, and event pages

[pettinarip]

Summary

• App pages (~3,696 URLs): Change @type from SoftwareApplication to WebApplication, add offers (free), map applicationCategory to schema.org enums
• Tutorial pages (25 URLs): Convert relative url fields to absolute URLs, truncate Course description to ≤60 chars for rich result eligibility
• Event pages (24-25 URLs): Change containedInPlace from LocalBusiness to Place (eliminates 5 warnings), add top-level startDate, add city-level address for Berlin hub

Context

Fixes structured data validation errors surfaced in the March 2026 Screaming Frog SEO audit. See docs/seo-audit-action-items.md for the full audit breakdown.

Issue	URLs affected	Fix
SoftwareApplication missing offers + review	3,696	Switch to WebApplication + add offers
Course url is relative, not absolute	25	Prepend SITE_URL
Course description exceeds 60 chars	25	Truncate to 60 chars
Event/EventSeries missing startDate	24-25	Add top-level startDate
Place missing address (Berlin hub)	25	Add city-level address
LocalBusiness wrong type for venue ref	25	Change to Place
Non-standard applicationCategory	3,696	Map to schema.org enums

Test plan

• Verify app page JSON-LD with Google Rich Results Test (e.g. /apps/uniswap/)
• Verify tutorial page JSON-LD shows absolute URLs (e.g. /developers/tutorials/)
• Verify events page JSON-LD includes startDate and Berlin address (e.g. /community/events/)
• TypeScript passes (npx tsc --noEmit)

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[myelinated-wackerow]

All changes are schema.org-accurate and correctly scoped. Type coverage is exhaustive (Record<AppCategory, string> enforces all 8 enum values). No UI, routing, or indexing regressions — JSON-LD only.

Key wins:

• ~3,696 app pages gain rich result eligibility via offers + WebApplication
• 25 tutorial URLs fixed (relative -> absolute) + Course descriptions trimmed
• Event pages lose 5+ validation warnings (Place, startDate, Berlin address)

Two things to consider @pettinarip (non-blocking):

1. startDate fallback uses build-time new Date() — works but changes every deploy and isn't semantically meaningful. Adding explicit start dates to hub schemas would be more durable.

2. 60-char Course description limit — worth confirming this is a hard Google requirement vs. a Screaming Frog heuristic. Harmless either way, but good to know.

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Reviewed by Claude Opus 4.6