Phase 6 구현: 커스텀 명령어 + i18n (ko/en)

- CustomInstructionService: 프리셋 5개 (번역/요약/전문리라이트/코드설명/자유프롬프트)
- 커스텀 명령어 CRUD + 프리셋 보호 (삭제 불가)
- CommandsPage: 명령어 목록 + 추가/편집 다이얼로그
- i18n: ko.json/en.json 리소스 파일, t() 함수, React 컨텍스트
- IPC: instruction 핸들러 6개
- AppLayout: Commands 네비게이션 추가

src/renderer/i18n/en.json

@@ -0,0 +1,58 @@
+{
+  "app.name": "D3RO Voice",
+  "nav.dashboard": "Dashboard",
+  "nav.history": "History",
+  "nav.dictionary": "Dictionary",
+  "nav.commands": "Commands",
+  "nav.settings": "Settings",
+  "dashboard.title": "Dashboard",
+  "dashboard.totalSessions": "Total Sessions",
+  "dashboard.totalTime": "Total Time",
+  "dashboard.totalWords": "Total Words",
+  "dashboard.streak": "Streak",
+  "dashboard.today": "Today",
+  "dashboard.sessions": "Sessions",
+  "dashboard.time": "Time",
+  "dashboard.words": "Words",
+  "history.title": "History",
+  "history.search": "Search transcriptions...",
+  "history.empty": "No history yet.",
+  "history.noResults": "No results found.",
+  "dictionary.title": "Dictionary",
+  "dictionary.search": "Search words...",
+  "dictionary.addWord": "Add Word",
+  "dictionary.empty": "No words yet. Add custom words for better STT accuracy.",
+  "dictionary.noResults": "No words found.",
+  "dictionary.word": "Word",
+  "dictionary.pronunciation": "Pronunciation (optional)",
+  "commands.title": "Custom Commands",
+  "commands.add": "Add Command",
+  "commands.name": "Name",
+  "commands.description": "Description",
+  "commands.prompt": "Prompt",
+  "commands.builtin": "Built-in",
+  "commands.custom": "Custom",
+  "settings.title": "Settings",
+  "settings.general": "General",
+  "settings.audio": "Audio",
+  "settings.stt": "STT",
+  "settings.llm": "LLM",
+  "settings.theme": "Theme",
+  "settings.language": "Language",
+  "settings.closeToTray": "Close to tray",
+  "settings.autoInsert": "Auto-insert text after transcription",
+  "settings.soundEffects": "Sound effects",
+  "settings.insertMethod": "Insert Method",
+  "settings.whisperModel": "Whisper Model",
+  "settings.sttLanguage": "Recognition Language",
+  "settings.ollamaUrl": "Ollama Server URL",
+  "common.cancel": "Cancel",
+  "common.save": "Save",
+  "common.delete": "Delete",
+  "common.add": "Add",
+  "common.edit": "Edit",
+  "common.close": "Close",
+  "common.loading": "Loading...",
+  "status.ollamaConnected": "Ollama Connected",
+  "status.ollamaOffline": "Ollama Offline"
+}