fix(bte panel): store BTE-relative thumbUrl so renderer's PROXY_BASE wrap doesn't double-encode

Browser console: 'Failed to load resource: ...%252Fb6078c89...%252Fimage:0'.
_refreshGrid normalized thumbUrl as a full proxy URL, then _renderGrid +
_renderDetail wrap it again with PROXY_BASE+encodeURIComponent → %2F →
%252F. Fix: store raw BTE path; let the existing renderer wrap it once.

Karpathy 4 rules: surface root cause (double-wrap, not the encoder),
smallest fix (one expression), surgical (no other shape change).

static/bte.js

@@ -369,7 +369,7 @@
           .filter((a) => a.brandId === state.brand || !state.brand || state.brand === "planb")
           .map((a) => ({
             id: a.id,
-            thumbUrl: a.hasImageData ? (PROXY_BASE + encodeURIComponent("/api/assets/" + a.id + "/image")) : null,
+            thumbUrl: a.hasImageData ? ("/api/assets/" + a.id + "/image") : null,
             lifecycle: a.status,
             ratingCount: 0,
             meanScore: a.visualPolishScore || a.brandFitScore || null,