feat(ui): add Turkish localization

[fitzgpt]

Adds Turkish (tr-TR) as a supported UI language, following the same structure as the existing German/Nepali localization (#523).

What's included

• packages/ui/src/lib/i18n/messages/tr/ — all 16 message modules + index.ts, mirroring the English files. 1,602/1,602 keys translated (verified against en/: no missing, no extra, every {placeholder} preserved).
• packages/ui/src/lib/i18n/index.tsx — tr added to the Locale union, SUPPORTED_LOCALES, and localeLoaders (lazy import, same as other locales).
• packages/ui/src/components/locale-selector.tsx — Türkçe added to the language options.
• CONTRIBUTING.md — translation-files row updated to list the current locale set.

Translation conventions

Following the repo's i18n rule ("add to en/ first, then every other locale"), plus the convention visible in existing locales:

• Developer jargon stays English: session, workspace, instance, provider, agent, prompt, token, diff, commit, worktree, branch, SideCar, plugin.
• Product names and acronyms stay literal: CodeNomad, OpenCode, GitHub, VS Code, API, CLI, SSH, TLS, TTS/STT.
• Turkish orthography (İ/ı casing, apostrophe suffixes on jargon: session'ın, agent'ler).

Verification

• npx tsc --noEmit -p tsconfig.json (packages/ui) — pass
• npx vite build (packages/ui) — pass (build also exercises mergeMessageParts, so no duplicate keys)
• Runtime check on vite dev: with a Turkish browser locale the app auto-detects and renders fully in Turkish; the language picker lists and selects Türkçe (screenshots below)

Screenshots

Before — English UI (fresh profile, en-US locale):

After — Turkish UI (auto-detected from browser locale):

After — language picker with Türkçe selected:

Reposting with corrected Markdown formatting.

[pascalandr]

Gatekeeper: two translation errors need correction before merge.

• packages/ui/src/lib/i18n/messages/tr/remoteAccess.ts:8,12-13 uses bağlanmak (connect), but these strings describe the server binding/listening on all interfaces or localhost. This reverses the networking operation and can mislead users about exposure. Please translate this as listening/binding instead.
• packages/ui/src/lib/i18n/messages/tr/messaging.ts:24-25 uses basılı tutma (press and hold), but this button toggles holding/pausing automatic follow for long replies; there is no press-and-hold gesture. Please translate the feature state rather than a gesture.

Everything else checked out: 1,602/1,602 keys, placeholders and markup preserved, tr-TR detection works, and UI typecheck/build pass. The Windows CI failure is an unrelated flaky concurrency test.

[fitzgpt]

Thanks for the careful review! Fixed both — binding now translated as listening, and hold as pausing automatic follow rather than a gesture.

[pascalandr]

Both requested translations are fixed, and the follow-up Eklentiler wording is correct. Rechecked the final head: all 1,602 keys and placeholders match, and UI typecheck/build pass.

The remaining Windows failure is the same unrelated concurrency test.

Thanks @fitzgpt !!