feat(i18n): add Ukrainian (uk) locale

[zerox9dev]

Summary

• Adds Ukrainian (uk) as a supported dashboard locale, per CONTRIBUTING.md'''s i18n guide: full translation under apps/dashboard/src/i18n/locales/uk/ (all 24 namespaces), registered in locales in apps/dashboard/src/i18n/index.ts, and the two Record<Locale, string> display-name maps (Settings > Language, onboarding language picker).
• Adds docs/i18n/README.uk.md (translated root README) and links it from the language-switcher badge row in the root README and every existing translation.
• Key and interpolation-placeholder ({name}, {count}, etc.) parity with en is exact across all 24 files — verified programmatically, not just by eye.
• Product/brand names, CLI commands, PEM certificate/key headers, and other technical strings are left untranslated, per the contributing guide.

Why UNTRANSLATED_BASELINE changed

The dashboard'''s own i18n-parity.test.ts ratchets a per-namespace count of locale strings that are byte-identical to English. Adding a 10th locale necessarily adds its own irreducible remainder to that count — this is not a translation gap, it'''s exactly the same class of exception every existing locale already has baked into that baseline: brand names (Openship Cloud/Edge/Mail, GitHub Releases, Amazon SES, Cloudflare Tunnel/R2, AWS S3, Backblaze B2, DigitalOcean Spaces, Microsoft Teams), literal technical strings that must not change (PEM headers, npm start, a pg_dump command, a mail-client name list), and placeholder-only templates with no actual prose (e.g. {greeting}, {name}, {status} → {hostname}). Every ordinary UI string in uk was translated — I audited every single uk value the parity checker flagged (bun run i18n:check --full) before touching the baseline, and fixed the ones that were genuinely missed (OAuth field labels, an SSH port label, a cron-expression subtitle, an account-switcher placeholder, etc.) rather than just raising the number to make the test pass.

Test plan

• Programmatic key-parity check: every uk/*.json has the exact same key set as its en/*.json counterpart (24/24 match).
• Programmatic placeholder-parity check: every {placeholder} occurrence count matches between en and uk (24/24 match).
• bun run i18n:check — reviewed the full untranslated-value diff for uk before adjusting the baseline (see above).
• bun run test (apps/dashboard) — 1186/1186 passing, including the updated i18n-parity.test.ts.
• bun run lint (tsc --noEmit, apps/dashboard) — no errors.