docs(agents): spell out tooling conventions (bunx, Bun-native APIs)

Three short lines added under Prerequisites so these conventions
live in the canonical agent context file instead of scattered
session memory:

- `bunx` over `npx`.
- Prefer native Bun APIs (Bun.Glob, Bun.file, Bun.write, Bun.$)
  over node:fs in repo scripts. Runtime is pinned by
  .tool-versions, so there's no Node-portability concern.
- Browser automation uses `bunx @playwright/cli` (not the
  deprecated `playwright-cli` package, not `npx playwright`).

Author: Brian M Hunt

AGENTS.md

@@ -43,7 +43,9 @@ Builds: `@tko/build.knockout` (backwards-compatible) and
 ## Prerequisites
 
 - **Bun** — package manager and script runner. Install via [mise](https://mise.jdx.dev/): `mise install` (reads `.tool-versions`), or [bun.sh](https://bun.sh).
-- Use `bun install` instead of `npm install`.
+- Use `bun install` instead of `npm install`; `bunx` instead of `npx`.
+- In repo scripts (`tko.io/scripts`, `tools/`, `builds/*/build.ts`), prefer native Bun APIs — `Bun.Glob`, `Bun.file`, `Bun.write`, `Bun.$` — over `node:fs`, `node:fs/promises.glob`, or ad-hoc `child_process`. Runtime is pinned by `.tool-versions`, so there's no Node-version portability concern.
+- Browser automation uses `bunx @playwright/cli <cmd>` (not `npx playwright`, not the deprecated `playwright-cli` package).
 
 ## Build Commands