chore(githooks): remove pre-push hook (#22956)

## Summary
- remove the `pre-push` git hook script from the repository
- remove the `make pre-push` target and related Makefile documentation
- update contributor and agent docs so they only describe the remaining
`pre-commit` hook

## Validation
- `make pre-commit`
- `git diff --check`

---
_Generated with [`mux`](https://github.com/coder/mux) • Model:
`openai:gpt-5.4` • Thinking: `high`_

scripts/githooks/pre-commit

@@ -3,7 +3,6 @@
 # Pre-commit hook that runs CI-equivalent checks locally.
 # Runs `make pre-commit` (gen, fmt, lint, typos, build) which
 # catches most CI failures without needing Docker or Playwright.
-# The full CI suite (including tests) runs via the pre-push hook.
 #
 # Installation (worktree-compatible):
 #