fix: remove token_uri image fallback in NFT pages

[pthmas]

Problem

Three frontend pages fall back to token.token_uri as an image URL when image_url is null:

• NFTContractPage.tsx:85 — token.image_url || token.token_uri || null
• NFTTokenPage.tsx:16 — token?.image_url || token?.token_uri || null
• AddressPage.tsx:335 — t.image_url || t.token_uri || null

token_uri is a URL to a JSON metadata document, not an image. The browser fetches JSON, fails to render it as an image, and shows a broken image icon — worse than the # placeholder shown when both are null.

Data confirms the fallback never helps. On Eden testnet across 114,951 indexed NFT tokens, there are zero cases where token_uri is a direct image URL:

token_uri type	count	has image_url
https:// (JSON metadata)	114,660	114,636
data:application/json;base64,...	127	0
NULL / empty	164	0

The backend already handles the one edge case where token_uri might point directly to an image: it checks content-type on fetch and stores it as image_url if image/* (metadata.rs:431-450). So by the time the frontend sees the data, image_url is always the correct field.

Fix

In all three locations, change:

const imageUrl = token.image_url || token.token_uri || null;

to:

const imageUrl = token.image_url || null;

Related

The tokens currently showing image_url = null are caused by separate backend bugs (#65, #66), not by missing frontend fallback logic.