Fix OG image size and quality (924x540 fallback, per-city export)

[AnayDhawan]

Problem

og.png fallback added in 7403d72 is 924x540, not the standard 1200x630 OG size. Left as a known follow-up in that commit. Per-city opengraph-image.tsx generation should also get a quality pass while touching this.

Scope

• Export proper 1200x630 og.png to replace the 924x540 fallback
• Re-check opengraph-image.tsx output (per-city dynamic OG images) for sizing/quality issues
• Spot-check unfurl on Facebook/X/WhatsApp/iMessage after the fix

Owner

@shauryagangrade