fix: rename lib/rework.js to .cjs for ESM compat

lib/rework.js uses module.exports (CJS) but Node treats .js as ESM
because root package.json has "type": "module". Rename to .cjs and
update require() paths in index.cjs and test/rework-rate.test.cjs.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: bradygaster

index.cjs

@@ -3,7 +3,7 @@
 const fs = require('fs');
 const path = require('path');
 
-const { calculatePrRework, calculateReworkSummary } = require('./lib/rework');
+const { calculatePrRework, calculateReworkSummary } = require('./lib/rework.cjs');
 
 const GREEN = '\x1b[32m';
 const RED = '\x1b[31m';

lib/rework.js lib/rework.cjslib/rework.js renamed to lib/rework.cjs

@@ -6,7 +6,7 @@ const { execFileSync } = require('child_process');
 const CLI = path.join(__dirname, '..', 'index.cjs');
 
 // Import rework calculation functions from the pure module (no CLI side effects)
-const { calculatePrRework, calculateReworkSummary } = require(path.join(__dirname, '..', 'lib', 'rework.js'));
+const { calculatePrRework, calculateReworkSummary } = require(path.join(__dirname, '..', 'lib', 'rework.cjs'));
 
 describe('calculatePrRework', () => {
   it('should return zero rework for PR with no reviews', () => {