fix: Bust full preview cache by etag

[hweihwang]

Summary

• add the file etag to generated Photos preview URLs handed to Viewer
• apply the same cache-busting to public album preview URLs
• commit rebuilt frontend assets expected by the Photos build workflow

Root cause

Photos passes Viewer a custom /apps/photos/api/v1/preview/{fileid}?x=4096&y=4096 URL. Viewer returns a supplied previewUrl unchanged before it reaches its own etag cache-busting path. Because Photos preview responses are cacheable, editing and overwriting an image can update the grid thumbnail while the full Viewer image still shows a stale cached preview.

Verification

• Browser repro on a Nextcloud 32.0.9 environment: after overwrite, the grid thumbnail had a new etag and edited dimensions, while the full Viewer image still loaded the no-etag Photos preview URL and old dimensions.
• Local before/after smoke on Nextcloud dev: base Photos build served full preview URL as /apps/photos/api/v1/preview/${fileid}?x=4096&y=4096; patched build served /apps/photos/api/v1/preview/${fileid}?etag=${etag}&x=4096&y=4096.
• Local Browser smoke on patched deployment: Photos page loaded the rebuilt index-CIY8HsG_.chunk.mjs asset and no longer loaded the old index-C6jH1auF.chunk.mjs asset after app-version cache key bump in the local deploy.
• make build-js-production with Node v24.14.0; re-running it left the worktree clean.
• git diff --check HEAD~1 HEAD

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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