[centralsofware]

## Description

Add complete Indonesian (`id`) locale translation to Seerr, enabling Bahasa Indonesia as a fully supported UI language.

Changes:
- **`src/i18n/locale/id.json`**: Complete translation file with all **1,714 keys** matching the English `en.json` reference. All placeholder variables (`{title}`, `{mediaServerName}`, `{relativeTime}`, etc.), ICU pluralization syntax, and HTML markup (`<strong>`, `<code>`, `<ProfileLink>`, etc.) are preserved.
- **`server/types/languages.ts`**: Register `'id'` in the `availableLocales` array so the backend recognizes `id` as a valid `AvailableLocale`.
- **`src/context/LanguageContext.tsx`**: Add `id: { code: 'id', display: 'Bahasa Indonesia' }` to `availableLanguages` so Indonesia appears in the Language Picker UI dropdown and notification settings.

## How Has This Been Tested?

- Validated `id.json` is valid JSON with exactly 1,714 keys — matching `en.json` key-for-key (no missing, no duplicate keys).
- Verified all real variable placeholders (`{title}`, `{mediaServerName}`, `{userCount}`, `{appDataPath}`, `{date}`, etc.) are preserved in translations.
- Verified ICU plural syntax (`plural`, `{count, plural, one {...} other {...}}`) is intact.
- Verified HTML markup (`<strong>`, `<code>`, `<ProfileLink>`, `<PlexWatchlistSupportLink>`, `<FindDiscordIdLink>`, etc.) is preserved.
- Confirmed existing translations already present in the original partial `id.json` were preserved unchanged.

## Screenshots / Logs (if applicable)

N/A — backend/i18n only change.

## Checklist:

- [x] I have read and followed the contribution [guidelines](https://github.com/seerr-team/seerr/blob/develop/CONTRIBUTING.md).
- [x] Disclosed any use of AI (see our [policy](https://github.com/seerr-team/seerr/blob/develop/CONTRIBUTING.md#ai-assistance-notice))
- [ ] I have updated the documentation accordingly.
- [ ] All new and existing tests passed.
- [ ] Successful build `pnpm build`
- [x] Translation keys validated (1,714/1,714 keys match `en.json`)
- [ ] Database migration (if required)