fix(metrics): Use 'characters' instead of 'KB' in chunk size comments

JS strings use UTF-16 encoding where character count != byte count.
Use 'K characters' for technical accuracy.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: yamadashy

src/core/metrics/calculateOutputMetrics.ts

@@ -2,9 +2,9 @@ import { logger } from '../../shared/logger.js';
 import { type MetricsTaskRunner, runTokenCount } from './metricsWorkerRunner.js';
 import type { TokenEncoding } from './TokenCounter.js';
 
-// Target ~200KB per chunk to balance tokenization throughput and worker round-trip overhead.
+// Target ~200K characters per chunk to balance tokenization throughput and worker round-trip overhead.
 // Benchmarks show 200K is the sweet spot: fewer round-trips than 100K with enough chunks
-// for good parallelism across available threads (e.g., 20 chunks for 4MB output on 4 cores).
+// for good parallelism across available threads (e.g., 20 chunks for a 4M character output).
 const TARGET_CHARS_PER_CHUNK = 200_000;
 const MIN_CONTENT_LENGTH_FOR_PARALLEL = 1_000_000; // 1MB
 

tests/core/metrics/calculateOutputMetrics.test.ts

@@ -173,7 +173,7 @@ describe('calculateOutputMetrics', () => {
       }),
     });
 
-    // With TARGET_CHARS_PER_CHUNK=200_000, 1.1MB content should produce 6 chunks
+    // With TARGET_CHARS_PER_CHUNK=200_000, 1.1M character content should produce 6 chunks
     const chunkSizes = processedChunks.map((chunk) => chunk.length);
 
     expect(processedChunks.length).toBe(6);