feat: show What's new in the interface language

[omartelo]

Summary

The What's new dialog parses CHANGELOG.md, so a user running lich in any language but English read the release notes in English. This translates them, per release, without touching CHANGELOG.md, which stays English and canonical (the release page still reads it).

• changelog/<locale>.md, one per interface language except English, holds only the latest release: a build only ever reads its own section, and git keeps the old ones. Embedded beside CHANGELOG.md.
• patchnotes.Current(locale) reads the locale's file and falls back to English when it is missing or translates another release (dev builds, a release cut without translating).
• Group names ("Added", "Fixed", the "2 fixed" counts) come from the catalogs in both windows, all 7 locales. Translations keep the ### headings in English: the windows color groups by the English word.
• TestTranslations holds every locale file to the latest release in CHANGELOG.md: one section under the same heading, same groups, item counts, alert kinds, code spans and bold lead-ins. A release cut without translating fails the gate.
• lich-changelog-i18n skill (versioned, .gitignore allowlist updated) is the procedure: slice the section, translate from English per locale (parallel, cheap model), keep headings, alert openers and code spans byte for byte, take interface words from the catalogs, run the test.
• 0.69.0 is translated as the first case. CLAUDE.md › Releases gains the step; the i18n rules in CLAUDE.md, frontend/CLAUDE.md and lich-i18n say where these translations live.

Known limit

In the native window, switching the interface language while the notes are loaded keeps them in the previous language until the window is reopened. The web window refetches (the resource key carries the locale).

Test plan

• go test ./internal/patchnotes: locale read, fallback for a missing locale and for a translation of another release, TestTranslations over the 6 real files
• native/: lichclient sends the locale; group labels and counts in pt-BR; catalog parity and plural forms
• Frontend: PatchNotesDialog.test.tsx renders the groups in pt-BR
• Local gate: biome ci, tsc, vite build, vitest with coverage, gofmt, go vet, go test (root and native/)
• Review a translated dialog in a real window: a dev build has no changelog section, so no -shot was taken