fix: properly organize shared test resources

- Move fixtures/ and unit/ to shared/ directory where they belong
- These test resources are used by both npm and native installations
- Update package.json test scripts to use new paths
- Fix relative import path in helpers.test.js
- All 46 npm-based tests now passing (7 unit + 5 integration + 34 npm)

Final test structure:
- native/     - Native installation tests only
- npm/        - npm package tests only
- shared/     - Shared utilities, fixtures, and unit tests
- integration/- Cross-installation integration tests
- edge-cases.sh/.ps1 - Master orchestrators

tests/shared/unit/helpers.test.js

@@ -0,0 +1,57 @@
+const assert = require('assert');
+const path = require('path');
+const os = require('os');
+const { expandPath, validateProfileName, isPathSafe } = require('../../../bin/helpers');
+
+describe('helpers', () => {
+  describe('expandPath', () => {
+    it('expands tilde to home directory', () => {
+      const expanded = expandPath('~/test');
+      assert.strictEqual(expanded, path.join(os.homedir(), 'test'));
+    });
+
+    it('expands environment variables', () => {
+      process.env.TEST_VAR = '/test/path';
+      const expanded = expandPath('${TEST_VAR}/file');
+      assert(expanded.includes('test'));
+      delete process.env.TEST_VAR;
+    });
+
+    it('handles Windows paths', () => {
+      if (process.platform === 'win32') {
+        const expanded = expandPath('%USERPROFILE%\\test');
+        assert(expanded.includes(os.homedir()));
+      }
+    });
+  });
+
+  describe('validateProfileName', () => {
+    it('accepts valid profile names', () => {
+      assert(validateProfileName('glm'));
+      assert(validateProfileName('sonnet-4-5'));
+      assert(validateProfileName('my_profile'));
+      assert(validateProfileName('profile123'));
+    });
+
+    it('rejects invalid profile names', () => {
+      assert(!validateProfileName('profile with spaces'));
+      assert(!validateProfileName('profile@special'));
+      assert(!validateProfileName('profile;injection'));
+    });
+  });
+
+  describe('isPathSafe', () => {
+    it('accepts safe paths', () => {
+      assert(isPathSafe('/usr/local/bin/claude'));
+      assert(isPathSafe('C:\\Program Files\\Claude\\claude.exe'));
+      assert(isPathSafe('/home/user/.local/bin/claude'));
+    });
+
+    it('rejects unsafe paths', () => {
+      assert(!isPathSafe('/usr/bin/claude; rm -rf /'));
+      assert(!isPathSafe('/usr/bin/claude|bash'));
+      assert(!isPathSafe('/usr/bin/claude&echo pwned'));
+      assert(!isPathSafe('/usr/bin/claude$(whoami)'));
+    });
+  });
+});