fix(recover): wrap embedded-manifest atob in try/catch for corrupt base64

[tmchow]

Summary

Wrap atob(personalization.manifestB64) in internal/html/assets/src/app.ts in a try/catch so a corrupted embedded manifest shows a toast instead of silently leaving Step 2 asking the user to load MANIFEST.age. Addresses #107.

Why

The whole point of embedding the manifest in recover.html is so the user doesn't need a separate MANIFEST.age file after their archive has been sitting on disk for years. If the base64 payload inside recover.html degrades (bit rot, truncated copy, storage corruption), atob throws a DOMException and the recovery page falls back to asking the user for a file that, by design, they may not have.

The existing flow at app.ts:341-349 had no error handler for that path, so:

• Step 2 tells the user "load MANIFEST.age," with no indication that the embedded copy is damaged.
• recover.html looks broken rather than specifically corrupted.

Changes

• internal/html/assets/src/app.ts: wrap the embedded-manifest decode in try { ... } catch (err) { showError(...) }. The success path is unchanged; on failure the user gets a toast whose guidance tells them to try another copy of recover.html or fall back to loading MANIFEST.age manually in Step 2.
• internal/translations/recover/en.json: add three keys — error_corrupt_embedded_manifest_title, error_corrupt_embedded_manifest_message, error_corrupt_embedded_manifest_guidance. Other locales fall back to English automatically (translations[currentLang][key] || translations['en'][key] || key in i18n.js:7), so no translator action is required to ship this; translators can add their own strings later via the normal flow.

Testing

• go test ./internal/translations/... — pass (existing parity test is opt-in via REMEMORY_CHECK_TRANSLATIONS=1).
• npx esbuild internal/html/assets/src/app.ts --bundle --format=iife --target=es2020 — clean build.
• npx tsc --noEmit — clean.
• Manual: with a hand-corrupted manifestB64 (swap a byte to !), the page now shows the "Corrupted embedded archive" toast and Step 2 still works via file upload.

Fixes #107

[eljojo]

thanks for submitting this fix!

PS: I made an edit to the PR description so it can fit the contribution guidelines. AI footers are not allowed on this repository.