feat(electrobun): i18n system — @formatjs/intl + Svelte 5 runes + 3 locales

- i18n.svelte.ts: store with $state locale + createIntl(), t() function,
  formatDate/Number/RelativeTime, getDir() for RTL, async setLocale()
- i18n.types.ts: TranslationKey union (codegen from en.json)
- locales/en.json: 200+ strings in ICU MessageFormat
- locales/pl.json: full Polish translation
- locales/ar.json: partial Arabic (validates 6-form plural + RTL)
- scripts/i18n-types.ts: codegen script for type-safe keys
- 6 components wired: StatusBar, AgentPane, CommandPalette,
  SettingsDrawer, SplashScreen, ChatInput
- Language selector in AppearanceSettings
- App.svelte: document.dir reactive for RTL
- CONTRIBUTING_I18N.md: guide for adding languages

Note: currently Electrobun-only. Will extract to @agor/i18n shared
package for both Tauri and Electrobun.

ui-electrobun/package.json

@@ -10,7 +10,8 @@
 		"hmr": "vite --port 9760",
 		"build:canary": "vite build && electrobun build --env=canary",
 		"test": "bun test src/bun/__tests__/",
-		"test:e2e": "wdio run tests/e2e/wdio.conf.js"
+		"test:e2e": "wdio run tests/e2e/wdio.conf.js",
+		"i18n:types": "bun scripts/i18n-types.ts"
 	},
 	"dependencies": {
 		"@codemirror/autocomplete": "^6.20.1",