chore(release): bump version to 0.8.0

[Nic-dorman]

Summary

• Promotes 0.8.0-rc.3 to stable 0.8.0
• Bumps version in 4 files: package.json, src-tauri/Cargo.toml, src-tauri/Cargo.lock, src-tauri/tauri.conf.json

Contents vs 0.7.1 (last stable)

• i18n Phase 1 (vue-i18n framework, EN + JA baseline, six locales total: en/ja/nl/fr/bg/es)
• CJK font install banner on Linux (feat(i18n): add CJK font install banner for Linux #139) — persistent dismissible banner with per-distro install commands and Copy buttons, shown when locale is ja on Linux
• Theme: native select popups follow dark mode on Linux (fix(theme): make native select popups follow dark theme on Linux #141) — color-scheme: dark on :root so the open <select> popup is painted dark by webkit2gtk
• ant-core 0.2.3 → 0.2.5 — merkle PUT timeout alignment + spill-dir leak fix on SIGKILL/OOM
• Plus the rc.1/rc.2/rc.3 cycle's docs and CI hygiene

Test plan

• Linux tester verified CJK font banner on ja locale (rc.3)
• Dropdown dark-mode fix merged to address rc.3 finding
• CI green on this bump PR
• After tag push: release CI builds stable installers for Win / Linux (AppImage / .deb / .rpm) / macOS (~22 min)
• Stable installer pulled via the in-app updater (without pre-release toggle) and verified to install cleanly

🤖 Generated with Claude Code

[Nic-dorman]

Closing — superseded. The rc.3 → 0.8.0 direct bump skipped the Korean locale addition. New flow: rc.3 → rc.4 (with ko) → verify → 0.8.0 stable.