fix(chat): keep remote image cards after turn-end remount

[Yy-702]

Why

Remote https images in assistant leftovers (e.g. a web-fetch stock chart) render while the answer is still streaming, then flip to 预览失败 — 文件可能已损坏或无法读取 (broken_blob) as soon as the turn ends.

The file is fine. Host already wrote a valid JPEG thumb under cache/image-thumbs/. What breaks is the remount:

1. session://journal_reconciled / ready rehydrates the journal and remounts ImageUi.
2. First paint uses the live https://… src.
3. resolveChatImageThumb hits the in-memory cache and swaps src to the loopback thumb in a microtask.
4. WKWebView aborts the in-flight https load → <img onError> → loadFailed is locked forever.

What

• First-paint chat cards from peekChatImageThumb when the session cache already has a display URL (no https → loopback swap on remount).
• Ignore abort / stale-src onError (shouldApplyChatImageLoadError); remount <img> with key={resolvedSrc}.
• Do not wipe a working https original when thumb resolve returns empty (nextChatCardDisplaySrc).

Verify

• pnpm exec vitest run src/lib/imageThumbClient.test.ts src/lib/mediaLoadPro.test.ts (42 passed)
• Local pnpm dev: reopen the morning-brief chat that showed the eastmoney chart; after the turn (and after switching away/back) the leftover card stays visible instead of “preview failed”.

[RongleCat]

Merged, thanks @Yy-702 — this is the right remount fix.

Journal rehydrate was first-painting the live https URL, then swapping to the cached loopback thumb and locking broken_blob on the WKWebView abort. First-paint from peekChatImageThumb, ignoring abort/stale-src, and keeping a working https original when thumb resolve is empty should keep leftover cards (charts, web-fetch images) visible after the turn ends.

Landed on main as 46429f3.