Summary

• persist completed file progress in a versioned localStorage entry scoped to the package, version range, and React Native Windows language
• identify files by their raw old/new diff paths, before app-name or package display replacements
• hydrate progress after the diff loads, ignore stale or malformed identifiers, and keep working in memory when browser storage is unavailable
• keep the existing UI unchanged; the optional reset control remains out of scope for this MVP

Closes #413

Test Plan

• yarn test --runInBand — 4 suites, 22 tests passed
• yarn lint
• yarn typecheck
• yarn build — production bundle compiled successfully
• yarn prettier --check on all changed files
• git diff --check
• Browser runtime with mocked upstream responses: mark a file complete, reload and confirm the Done section is restored; switch from 0.63.2→0.64.2 to 0.63.2→0.64.1 and confirm progress is isolated; switch back and confirm it is restored

The browser run also surfaced existing React DOM-prop warnings from DiffComment for isCommentOpen and lineChangeType. This PR does not touch that component and introduced no new console warning.

What are the steps to reproduce?

1. Select a current and target React Native version.
2. Mark one or more diff files as viewed.
3. Reload the page or leave and return later.
4. The same files remain in the Done section for that exact upgrade context.
5. Select another version range or platform; its progress starts independently.

Checklist

• I tested this thoroughly
• README documentation is not needed because this preserves an existing workflow without adding a new control or public API