docs: translate design.md, refresh state for v0.2.0, add badge

[Avers]

Docs only — no code changes.

1. docs/design.md translated to English

The 1124-line design document was entirely in Russian. Full translation
to English with the structure verified identical to the original:
47 headers (same order), 66 code blocks, 5 blockquotes, 39 horizontal
rules. ASCII diagrams translated in place (labels only, layout kept),
code kept as-is, technical terms (LBA, FTL, ECC, wear leveling) preserved.

2. Version alignment / state refresh

• New Round 8 — Binary Release Pipeline (PRs ci(release): build per-OS/arch binary tarballs on tag #17–ci(release): build the Intel macOS tarball on macos-15-intel #22): the release
  workflow, the macos-13 retirement (2025-12-04), the unique-artifact-name
  fix, and the published v0.2.0 release (four tarballs + .sha256,
  verified end-to-end)
• What's Next: "Tag and push v0.2.0" is done — replaced with the
  current queue (remove the temporary sudoers file, glibc ≥ 2.38 coverage
  for the Linux tarballs, read-ahead --resume test)
• Landed this session: extended with the binary release pipeline
• README download links were already at v0.2.0

3. Badge before the README title

+<img src="badge.svg" width="72" alt="flashcheck logo">
+
 # flashcheck