fix(i18n): keep saved language on font failure, tighten CJK font matching

- Web: a failed CJK font fetch shows English for this session only; the
  saved language preference is kept (CjkFontLoader, persisted on save).
- Web fetches the CJK font only when a CJK language (ja) is selected.
- fonts.rs: directory scans match CJK-specific names only (no "noto" or
  "gothic"); CJK stays the last fallback after the Latin UI font.
- Revert unrelated clippy rewrites in component_clone.rs, coplanar.rs,
  canvas.rs and issue_report.rs to match main.
- Tests: default English, fallback order, CJK-only matching, fetch only
  for CJK, failed fetch keeps the saved language.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01RjGw4gA5ZvKrU8MQP6sBgT

docs/localization.md

@@ -39,8 +39,8 @@ In the browser, `solvecraft-web` bundles a self-hosted Japanese font (`BIZUDPGot
 under SIL OFL 1.1) within the web distribution artifacts only. The font is loaded asynchronously from the same
 origin (`./fonts/BIZUDPGothic-Regular.ttf`) on-demand when the interface language is set to Japanese, without
 contacting any external CDNs or third-party servers. For users with an English interface, no font download
-occurs. If font loading fails, the web interface gracefully falls back to English to prevent missing glyphs
-(tofu). This bundled font specifically targets Japanese; Korean (Hangul) and Chinese scripts are not covered.
+occurs. If font loading fails, the web interface shows English for that session only to prevent missing
+glyphs (tofu); the saved language preference is kept, so the next visit tries again. This bundled font specifically targets Japanese; Korean (Hangul) and Chinese scripts are not covered.
 
 The current messages support named substitution, not locale-specific plural selection,
 number/date formatting, or right-to-left layout and shaping. Add those capabilities when