perf: speed up slow git tests from ~18s to ~5.5s

- branch-manager: beforeEach→beforeAll (all 12 tests are read-only)
- worktree manager: clone template repo per test instead of full init
- signal-manager: reduce setTimeout delay from 100ms to 30ms

apps/server/git/simple-git-branch-manager.test.ts

@@ -5,7 +5,7 @@
  * a project's default branch.
  */
 
-import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { describe, it, expect, beforeEach, afterEach, beforeAll, afterAll } from 'vitest';
 import { mkdtemp, rm, writeFile } from 'node:fs/promises';
 import { tmpdir } from 'node:os';
 import path from 'node:path';
@@ -133,14 +133,14 @@ describe('SimpleGitBranchManager', () => {
   let cleanup: () => Promise<void>;
   let branchManager: SimpleGitBranchManager;
 
-  beforeEach(async () => {
+  beforeAll(async () => {
     const setup = await createTestRepoWithRemote();
     clonePath = setup.clonePath;
     cleanup = setup.cleanup;
     branchManager = new SimpleGitBranchManager();
   });
 
-  afterEach(async () => {
+  afterAll(async () => {
     await cleanup();
   });
 
@@ -177,14 +177,14 @@ describe('SimpleGitBranchManager - diffBranchesStat and diffFileSingle', () => {
   let cleanup: () => Promise<void>;
   let branchManager: SimpleGitBranchManager;
 
-  beforeEach(async () => {
+  beforeAll(async () => {
     const setup = await createTestRepoForDiff();
     clonePath = setup.clonePath;
     cleanup = setup.cleanup;
     branchManager = new SimpleGitBranchManager();
   });
 
-  afterEach(async () => {
+  afterAll(async () => {
     await cleanup();
   });