docs: Rename CLAUDE.md to AGENTS.md and update e2e guidance (#1453)

Author: timfish

AGENTS.md

@@ -0,0 +1,28 @@
+# Agent guidance for sentry-electron
+
+## Running the e2e tests
+
+The end-to-end tests in [`test/e2e`](./test/e2e) launch real Electron apps. A few things are required to run them
+successfully, especially from an agent shell such as Claude Code:
+
+- **`unset ELECTRON_RUN_AS_NODE` first.** Some agent shells, such as Claude Code, export `ELECTRON_RUN_AS_NODE=1`,
+  which makes every Electron binary run as plain Node. When that happens `require('electron').app` is `undefined` and
+  every test crashes at SDK load (`normalize.js` calling `app.getAppPath()`) or times out. This is not a broken
+  harness — it only affects shells where that variable is set.
+- **Set `ELECTRON_VERSION`.** The runner throws `ELECTRON_VERSION is not set` otherwise. The SDK needs Electron 35 or
+  higher, so use a version in that range whose binary is already cached (e.g. `39.8.10`).
+- **Build and pack the SDK first.** The test apps install `sentry-electron-v<version>.tgz` from the repo root, and
+  `yarn e2e` does not create it. Run `yarn build && yarn pack` after each change to `src`.
+- **Use `yarn e2e`, not a bare `vitest` invocation.** `yarn e2e` runs the `pree2e` step (`set-version`, cache cleanup)
+  that the tests depend on.
+- **`-t` is a regex**, so escape parentheses in test names, e.g. `-t 'Browser Tracing \(Span streaming\)'`.
+- **`DEBUG=true`** prints every received envelope as `[Test Runner] Received event ...`, which is the easiest way to
+  build/verify assertions.
+
+Example — run all span-streaming tests against Electron 39.8.10:
+
+```shell
+unset ELECTRON_RUN_AS_NODE
+yarn build && yarn pack
+DEBUG=true ELECTRON_VERSION=39.8.10 yarn e2e -t 'Span streaming'
+```