chore: add PR conventions note to AGENTS.md (#5166)

## Changes Made

- Add PR conventions note to AGENTS.md
- Add CLAUDE.md symlink to AGENTS.md

## Related Issues

- Related PR: #5124

## Checklist

- [x] Documentation builds and is formatted properly (tag @/ccmao1130
for docs review)

Author: ykdojo

AGENTS.md

@@ -24,3 +24,8 @@
     - `make test EXTRA_ARGS="-v tests/dataframe/test_select.py::test_select_dataframe"` runs the given test method.
   -  Default `integration`, `benchmark`, and `hypothesis` tests are disabled. Best to run on CI.
 - `make doctests` runs doctests in `daft/` directory. Tests docstrings in Daft APIs.
+
+## PR Conventions
+
+- Titles: Conventional Commits (e.g., `feat: ...`); enforced by `.github/workflows/pr-labeller.yml`.
+- Descriptions: follow `.github/pull_request_template.md`.

CLAUDE.md

@@ -0,0 +1 @@
+AGENTS.md