agents: specify docs and build(release) commit types (#4095)

Ambiguity in commit type selection can cause issue templates or release
scripts to be mislabeled under generic types like chore.

Updates the agent pull request rules to specify that issue template
changes use docs: and release tooling uses build(release):.

.agents/rules/pr.md

diff --git a/.agents/rules/pr.md b/.agents/rules/pr.md
index 9e5fa9d..ae75aa3 100644
--- a/.agents/rules/pr.md
+++ b/.agents/rules/pr.md
@@ -16,9 +16,10 @@
 
 ## Commit & PR Types
 * `fix:` / `feat:`: User-visible changes ONLY.
-* `build:` / `build(release):`: Internal release tooling, developer workflows,
-  and build scripts (prefer `build(release):` over `chore:` or `tools:`, since
-  `tools:` could be ambiguous with production tools).
+* `build:` / `build(release):`: Internal release tooling
+  (`tools/private/release/`), developer workflows, and build scripts. Always
+  prefer `build(release):` over `chore:` or `chore(release):`.
+* `docs:`: Documentation and issue templates (`.github/ISSUE_TEMPLATE/`).
 * `ci:`: `.bazelci` and Buildkite CI configurations.
 * `workflow:` / `workflows:`: GitHub Actions workflow configurations
   (`.github/workflows/`).