Add native Vicinae caffeinate extension

Keeps the computer awake from Vicinae. Written against @vicinae/api
directly because the Raycast `coffee` extension cannot work here:

- Its `index` command is `menu-bar` mode, which Vicinae does not support.
- Its `status` command crashes on `Cannot read properties of null
  (reading 'IsManuallyDecafed')` because it gates on
  `LocalStorage.getItem(key) === undefined`. Vicinae resolves a missing
  key to `null`, not `undefined` (verified with a runtime probe).

Sleep prevention is an OS-level assertion, so the extension delegates and
gets out of the way:

- macOS:  caffeinate -i [-d] [-s] [-t <seconds>]
- Linux:  systemd-inhibit --what=idle:sleep --why=<reason> sleep <n|infinity>

The process is spawned detached + unref'd, because Vicinae unloads a
no-view command as soon as its function returns. Timed sessions need no
babysitter: `caffeinate -t` and `sleep <n>` self-terminate.

Commands: toggle (no-view), status (view), caffeinate-for (view).

Two deliberate safety choices:
- Stopping signals the recorded PID rather than running `killall
  caffeinate`, so a caffeinate the user started themselves survives.
  Verified against a real concurrent `caffeinate -u -dmi` process.
- The PID's name is re-checked with `ps -o comm=` before signalling, since
  PIDs get recycled and a stale entry could otherwise kill something
  unrelated.

Also: display-sleep prevention is macOS-only, and the UI says so on Linux
rather than pretending systemd-inhibit can hold the display awake.

Verified: vici lint, tsc --noEmit, eslint, 23/23 vitest, vici build, and
live in Vicinae — toggle starts `caffeinate -i` which survives the
command unloading, toggle again stops only ours, both view commands load
with clean stdout/stderr.

src/toggle.ts

@@ -0,0 +1,15 @@
+import { Toast, showHUD, showToast } from "@vicinae/api";
+import { toggleCaffeination } from "./lib/caffeinate";
+
+export default async function ToggleCaffeination() {
+  try {
+    const result = await toggleCaffeination();
+    await showHUD(result === "stopped" ? "☕ Sleep is allowed again" : "☕ Staying awake");
+  } catch (error) {
+    await showToast({
+      style: Toast.Style.Failure,
+      title: "Could not change caffeination",
+      message: error instanceof Error ? error.message : String(error),
+    });
+  }
+}