HackDigest v0.3.1

Alignment release: the docs catch up with what v0.3.0 already ships, the
site joins the family dark-mode baseline, and the updater's download loop
gains a watchdog. No app-facing behavior changes beyond the hardening.

Added

• Download watchdog in the updater: a transfer that stops making byte
  progress for 120 seconds, or that runs past a 30-minute wall-clock
  total, is broken out of its worker (exn:break), the .partial file is
  cleaned up, and the phase lands on error — the UI always gets a terminal
  state instead of resting on "downloading" forever.
• User guide: docs/guide.html on the product site — five-minute start,
  engine and BYOK setup, reading preferences, shortcuts, and FAQ
  (data location, privacy, platforms, updates incl. the 0.2.x path,
  uninstall). Bilingual via data-i18n, default Chinese.

Changed

• README (English and Chinese) now describes the updater as it actually
  works since v0.3.0: startup fetch of the Ed25519-signed manifest,
  in-place swap on macOS/Windows portable installs, download-and-reveal on
  Linux, release page for installer channels — replacing the stale
  "in-place updates wait on glaze#47" wording. The download table shows
  the real v0.3.0 Linux matrix (tar.gz / deb / rpm / AppImage / zip, every
  format on both architectures, per-asset .sha256 sidecars).
• CI and release workflows pin glaze to v0.13.1 (.git-suffixed URL)
  instead of a floating branch install.
• Product site: palette aligned to the family values (#faf7f2 /
  #c15f3c / #e8e2d9 …), full dark mode with a manual toggle,
  localStorage persistence and a head anti-flash script, and download
  copy that matches the real update flow. docs/GLAZE-MIGRATION.md is
  marked as completed with a pointer to the CHANGELOG.