docs: add note about tricky code comments

AGENTS.md

@@ -25,6 +25,7 @@
 ## Coding Style & Naming Conventions
 - Language: TypeScript (ESM). Prefer strict typing; avoid `any`.
 - Formatting/linting via Biome; run `pnpm lint` before commits.
+- Add brief code comments for tricky or non-obvious logic.
 - Keep files concise; extract helpers instead of “V2” copies. Use existing patterns for CLI options and dependency injection via `createDefaultDeps`.
 - Aim to keep files under ~700 LOC; guideline only (not a hard guardrail). Split/refactor when it improves clarity or testability.