fix: electron 28→40 migration fixes

- Replace deprecated fs.rmdir with fs.rm (Node 22+ deprecation)
- Update electron-builder 25.1.8 → 26.8.1 (required for Electron 35+)
- Add macOS minimumSystemVersion 12.0 (Electron 38+ requirement)
- Update React 18 → 19 in README.md tech stack

README.md

@@ -243,7 +243,7 @@ Yes. Run multiple teams in one project or across different projects, even simult
 
 ## Tech stack
 
-Electron 40, React 18, TypeScript 5, Tailwind CSS 3, Zustand 4. Data from `~/.claude/` (session logs, todos, tasks). No cloud backend — everything runs locally.
+Electron 40, React 19, TypeScript 5, Tailwind CSS 3, Zustand 4. Data from `~/.claude/` (session logs, todos, tasks). No cloud backend — everything runs locally.
 
 <details>
 <summary><strong>Build from source</strong></summary>

package.json

@@ -177,7 +177,7 @@
     "@vitest/coverage-v8": "^3.1.4",
     "autoprefixer": "^10.4.17",
     "electron": "^40.3.0",
-    "electron-builder": "^25.1.8",
+    "electron-builder": "^26.8.1",
     "electron-vite": "^2.3.0",
     "eslint": "^9.39.2",
     "eslint-config-prettier": "^10.1.8",
@@ -244,6 +244,7 @@
     },
     "mac": {
       "category": "public.app-category.developer-tools",
+      "minimumSystemVersion": "12.0",
       "target": [
         "dmg",
         "zip"

src/main/services/extensions/skills/SkillPlanService.ts

@@ -401,7 +401,7 @@ export class SkillPlanService {
         if (entries.length > 0) {
           return;
         }
-        await fs.rmdir(nextDir);
+        await fs.rm(nextDir);
       } catch {
         return;
       }

src/main/services/team/TeamTaskAttachmentStore.ts

@@ -180,7 +180,7 @@ export class TeamTaskAttachmentStore {
     try {
       const entries = await fs.promises.readdir(dir);
       if (entries.length === 0) {
-        await fs.promises.rmdir(dir);
+        await fs.promises.rm(dir);
       }
     } catch {
       // ignore cleanup errors