feat(03-01): add skill section type wiring, Zustand slice, i18n, and sidebar nav entry

- Add "skills" to SectionId union in shared types
- Add SkillRecord, SkillImportResult, SkillUpdateStatus types to shared/types.ts
- Create SkillSlice with skills list, selection, file path, and import modal state
- Wire SkillSlice into Zustand store composition
- Add "nav.skills" i18n keys for English and Chinese
- Add Skills sidebar nav entry with PuzzlePiece icon between Communication and Documents
- Add section === "skills" rendering route in App.tsx
- Clear skill state on company switch
- Add skills case to navigateTo in NavigationSlice

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/renderer/i18n/en.ts

@@ -22,6 +22,7 @@ export const en: Record<string, string> = {
   "nav.costs": "Costs",
   "nav.activity": "Activity",
   "nav.social": "Social Media",
+  "nav.skills": "Skills",
   "nav.connectors": "Connectors",
   "nav.workspaces": "Workspaces",
   "nav.settings": "Settings",

src/renderer/i18n/zh.ts

@@ -22,6 +22,7 @@ export const zh: Record<string, string> = {
   "nav.costs": "成本",
   "nav.activity": "活动",
   "nav.social": "社交媒体",
+  "nav.skills": "技能",
   "nav.connectors": "连接器",
   "nav.workspaces": "工作区",
   "nav.settings": "设置",