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/components/skills/SkillsSection.tsx

@@ -0,0 +1,15 @@
+import type { AgentRecord } from "@shared/types";
+
+interface SkillsSectionProps {
+  companyId: string;
+  agents: AgentRecord[];
+  onRefresh: () => void;
+}
+
+export function SkillsSection({ companyId: _companyId, agents: _agents, onRefresh: _onRefresh }: SkillsSectionProps) {
+  return (
+    <div className="h-full">
+      <p className="text-[color:var(--muted)]">Skills section placeholder -- Task 2</p>
+    </div>
+  );
+}

src/renderer/components/skills/index.ts

@@ -0,0 +1 @@
+export { SkillsSection } from "./SkillsSection";