feat(linkedin): add clipboard-helper.mjs — cross-platform clipboard utility

TDD: 13 tests written first, then implementation.
Exports copyToClipboard(text) and clipboardAvailable() — never throws.
Supports darwin (pbcopy), win32 (clip), linux (xclip/xsel fallback).
Dual standalone/import mode following personalization-score.mjs pattern.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

plugins/linkedin-thought-leadership/hooks/scripts/__tests__/clipboard-helper.test.mjs

@@ -0,0 +1,86 @@
+import { describe, test } from 'node:test';
+import assert from 'node:assert/strict';
+import { clipboardAvailable, copyToClipboard } from '../clipboard-helper.mjs';
+
+describe('clipboardAvailable', () => {
+  test('returns object with available and platform fields', () => {
+    const result = clipboardAvailable();
+    assert.equal(typeof result.available, 'boolean');
+    assert.equal(typeof result.platform, 'string');
+  });
+
+  test('returns available: true on macOS (darwin)', () => {
+    if (process.platform !== 'darwin') return;
+    const result = clipboardAvailable();
+    assert.equal(result.available, true);
+    assert.equal(result.platform, 'darwin');
+  });
+
+  test('returns a recognized platform string', () => {
+    const result = clipboardAvailable();
+    assert.ok(
+      ['darwin', 'win32', 'linux'].includes(result.platform),
+      `Unexpected platform: ${result.platform}`
+    );
+  });
+});
+
+describe('copyToClipboard', () => {
+  test('returns object with success and platform fields', () => {
+    const result = copyToClipboard('test clipboard text');
+    assert.equal(typeof result.success, 'boolean');
+    assert.equal(typeof result.platform, 'string');
+  });
+
+  test('copies text successfully on macOS', () => {
+    if (process.platform !== 'darwin') return;
+    const result = copyToClipboard('clipboard-helper test 2026');
+    assert.equal(result.success, true);
+    assert.equal(result.platform, 'darwin');
+  });
+
+  test('handles empty string input gracefully', () => {
+    const result = copyToClipboard('');
+    assert.equal(result.success, true);
+    assert.equal(typeof result.platform, 'string');
+  });
+
+  test('handles multiline text', () => {
+    const multiline = 'Line 1\nLine 2\nLine 3';
+    const result = copyToClipboard(multiline);
+    assert.equal(result.success, true);
+  });
+
+  test('handles special characters (quotes, ampersands, backticks)', () => {
+    const special = 'He said "hello" & she said \'goodbye\' `code` $VAR';
+    const result = copyToClipboard(special);
+    assert.equal(result.success, true);
+  });
+
+  test('handles unicode/emoji text', () => {
+    const unicode = '🚀 Thought leadership → impact';
+    const result = copyToClipboard(unicode);
+    assert.equal(result.success, true);
+  });
+
+  test('never throws — always returns a result object', () => {
+    assert.doesNotThrow(() => copyToClipboard(null));
+    assert.doesNotThrow(() => copyToClipboard(undefined));
+    assert.doesNotThrow(() => copyToClipboard(123));
+  });
+
+  test('returns success: false for non-string input', () => {
+    const result = copyToClipboard(null);
+    assert.equal(result.success, false);
+  });
+});
+
+describe('module exports', () => {
+  test('exports clipboardAvailable as a function', () => {
+    assert.equal(typeof clipboardAvailable, 'function');
+  });
+
+  test('exports copyToClipboard as a function', () => {
+    assert.equal(typeof copyToClipboard, 'function');
+  });
+});