Accept text/plain events from the Plausible tracker

The Plausible tracker posts its JSON payload with Content-Type text/plain,
  which Laravel does not parse, so every real event failed validation and
  was redirected instead of being forwarded.

  - Decode the raw body when the request is not JSON
  - Respond with 400 instead of a redirect on invalid non-JSON requests
  - Trim trailing slash from the configured domain when forwarding events
  - Add a 5s timeout and respond with 502 when Plausible is unreachable

tests/PlausibleProxyTest.php

@@ -1,5 +1,6 @@
 <?php
 
+use Illuminate\Http\Client\ConnectionException;
 use Illuminate\Support\Facades\Http;
 
 it('fetches plausible script and caches it', function () {
@@ -145,3 +146,56 @@ it('rejects invalid props', function () {
         'p' => 'not-json',
     ])->assertStatus(422)->assertJsonValidationErrors(['p']);
 });
+
+it('accepts events sent as text/plain by the plausible tracker', function () {
+    Http::fake([
+        'https://plausible.io/api/event' => Http::response('ok', 202),
+    ]);
+
+    $this->call('POST', '/api/event', [], [], [], ['CONTENT_TYPE' => 'text/plain'], json_encode([
+        'n' => 'pageview',
+        'u' => 'https://example.com/page',
+        'd' => 'example.com',
+        'r' => null,
+    ]))->assertStatus(202);
+
+    Http::assertSent(fn ($request) => $request->url() === 'https://plausible.io/api/event'
+        && $request['n'] === 'pageview'
+        && $request['u'] === 'https://example.com/page'
+        && $request['d'] === 'example.com');
+});
+
+it('responds with 400 for invalid text/plain events', function () {
+    Http::fake();
+
+    $this->call('POST', '/api/event', [], [], [], ['CONTENT_TYPE' => 'text/plain'], 'not-json')
+        ->assertStatus(400);
+
+    Http::assertNothingSent();
+});
+
+it('handles a trailing slash in the domain when forwarding events', function () {
+    config()->set('plausible-proxy.domain', 'https://plausible.example.com/');
+
+    Http::fake([
+        'https://plausible.example.com/api/event' => Http::response('ok', 202),
+    ]);
+
+    $this->postJson('/api/event', [
+        'n' => 'pageview',
+        'u' => 'https://example.com/page',
+        'd' => 'example.com',
+    ])->assertStatus(202);
+
+    Http::assertSent(fn ($request) => $request->url() === 'https://plausible.example.com/api/event');
+});
+
+it('responds with 502 when plausible is unreachable', function () {
+    Http::fake(fn () => throw new ConnectionException('Connection refused'));
+
+    $this->postJson('/api/event', [
+        'n' => 'pageview',
+        'u' => 'https://example.com/page',
+        'd' => 'example.com',
+    ])->assertStatus(502);
+});