refactor: remove ~70 low-value comments across 13 files

- Remove empty section markers (// === ... ===, // --- ... ---) that duplicate JSDoc or function names
- Remove "what" comments that restate the next line of code (e.g. // Save to disk, // Check for retryable patterns)
- Remove file-level descriptions that restate the filename (e.g. // Pure functions for formatting console output)
- Fix "Added by client" comment referencing implementation history → "Used for audit correlation"
- Preserve all WHY comments: error classification groups, billing/session limit explanations, ESM interop, exactOptionalPropertyTypes, mutex reasoning

src/utils/metrics.ts

@@ -4,8 +4,6 @@
 // it under the terms of the GNU Affero General Public License version 3
 // as published by the Free Software Foundation.
 
-// Timing utilities
-
 export class Timer {
   name: string;
   startTime: number;