fix(app): complete translation coverage

[opencode-agent]

Summary

• add the eight missing session-export strings to all 27 non-English app locales
• localize the usage-limit “Don't show again” action across every supported locale
• render the titlebar update label from the existing translation key instead of hardcoded English
• run full dictionary and placeholder parity in CI instead of skipping the suite when CI is set
• document the invariant that product code stays locale/plural unaware behind typed t / plural / native-bundle APIs

Audit evidence

The audit compared all app, UI, and desktop dictionaries against English on dev at b7f9363393c4 and scanned production TS/TSX for user-visible literals.

Before this change:

• all 27 non-English app dictionaries were missing the same eight session-export keys, producing 216 English fallbacks
• DialogUsageExceeded rendered “Don't show again” directly in English
• the titlebar update pill computed translated titlebar.update / titlebar.updateVersion values but still rendered a literal Update
• the comprehensive parity suite used describe.skipIf(!!process.env.CI), allowing dictionary drift through CI

After this change:

• all supported app, UI, and desktop locales have key parity with their English source dictionaries
• placeholders and locale-specific plural variants remain aligned
• the usage-limit action and update pill use locale dictionaries
• parity now executes with CI=true

Translation method

Translations were researched in independent locale groups and reconciled against:

• existing OpenCode locale dictionaries and established terminology for session, export, save, and errors
• Unicode CLDR locale and plural guidance
• Microsoft, Apple, and Mozilla localization guidance and terminology
• Mozilla Pontoon and the Firefox localization corpus
• relevant language authorities, including Duden, RAE/Fundéu, FranceTerme/Académie française, Dansk Sprognævn, Språkrådet, Nederlandse Taalunie, Accademia della Crusca, Kotus, Institutet för språk och folkminnen, PWN/Rada Języka Polskiego, Russian and Arabic language references, Ukrainian academic guidance, Taiwan MOE conventions, Royal Society-oriented Thai terminology, and TDK

The English source remains unchanged except for the new key that captures the existing hardcoded “Don't show again” copy. {{filename}} is preserved exactly in every locale. Arabic, Urdu, and Shahmukhi Punjabi wrap the interpolated filename with Unicode FSI/PDI isolates to keep unknown-direction filenames readable in RTL sentences.

Locale coverage

Updated ar, az, br (pt-BR), bs, da, de, es, fi, fr, hi, id, it, ja, ko, nl, no (nb-NO), pa (Shahmukhi Punjabi), pl, ru, sv, th, tr, uk, ur, vi, zh, and zht (Traditional Chinese/Taiwan).

Checks

• CI=true bun test ./src/i18n/parity.test.ts ./src/i18n/desktop-native.test.ts — 8 passed, 0 failed, 442 assertions
• bun typecheck from packages/app — passed
• scoped oxlint — 0 errors (existing warnings remain outside this change)
• git diff --check — passed
• post-fix production-string scan — targeted hardcoded usage action and update label no longer present

Requested by: @Hona (Hona via Slack)