docs: require workaround comments in AGENTS (#274)

## Summary
- add a repository-wide rule to document workaround context in code
comments
- require comments to explain why the workaround exists, its scope, and
removal conditions

## Testing
- not run (docs-only change)

Author: kdy1

AGENTS.md

@@ -5,6 +5,7 @@
 - List files in `docs/` before starting each task, and keep `docs/` up-to-date.
 - After completing each task, update the relevant `AGENTS.md` and `docs/` files in the same change when policies, structure, or contracts changed.
 - Write all code and comments in English.
+- When introducing a workaround, leave sufficient comments that explain why it exists, its scope, and the conditions for removing it.
 - Prefer enum types over strings whenever possible.
 - If you modified Rust code, run `cargo test` from the root directory before finishing your task.
 - If you modified frontend code, run `pnpm test` from the frontend directory before finishing your task.