fix(desktop): render splash pages as UTF-8

[Ishaan Gangwani (ishaan1124)]

Summary

• declare UTF-8 on every inline Electron desktop document
• prevent the splash ellipsis and Unicode startup errors from rendering as mojibake
• add a regression contract covering all three inline pages

Test Coverage

All changed paths are covered by the desktop shell contract. The regression rejects the prior unqualified data:text/html, form and pins all three UTF-8 documents.

Pre-Landing Review

No issues found. Independent review confirmed the MIME charset fixes the exact %E2%80%A6 → … failure mode.

Design Review

No design issues found; this preserves the existing splash layout and corrects text decoding only.

Verification

• 32 desktop installer/updater/shell tests pass
• node --check frontend/desktop/src/main.mjs
• scoped Prettier check
• git diff --check

Release

No source version/changelog edit: this repository's signed publish workflow creates the patch release commit and changelog metadata after merge.

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Project	Deployment	Actions	Updated (UTC)
openscience	Ready	Preview	Aug 30, 2026 7:48am