Add a Publisher abstraction and queued job to publish from the UI

Introduce Publisher/PublisherManager (WordPress + Reddit implementations)
so publishing logic is shared between the CLI, the queue, and future
network integrations. Add a "Publish" button on the Posts page that
dispatches PublishPostJob instead of blocking the request — Reddit's
publisher shells out to the existing Playwright sidecar and can take
tens of seconds, so it can't run synchronously in a web request.

Adds a `target` field (e.g. subreddit) and `publishing` status to Post,
plus a `publish_error` field so failures surface in the UI. Refactors
posts:publish to delegate to WordPressPublisher without changing its
CLI output contract (existing tests pass unchanged).

Also fixes two bugs found along the way: UpdatePostRequest was silently
dropping `published_url` from PATCH requests (never in its validation
rules, despite AI_API.md documenting it), and three Livewire index-page
tests were broken by the earlier auth change (never re-run after adding
the `auth` middleware) since they hit routes via HTTP without a logged-in
user.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/Providers/AppServiceProvider.php

@@ -2,6 +2,9 @@
 
 namespace App\Providers;
 
+use App\Support\Publishing\PublisherManager;
+use App\Support\Publishing\RedditPublisher;
+use App\Support\Publishing\WordPressPublisher;
 use Illuminate\Support\ServiceProvider;
 
 class AppServiceProvider extends ServiceProvider
@@ -11,7 +14,10 @@ class AppServiceProvider extends ServiceProvider
      */
     public function register(): void
     {
-        //
+        $this->app->singleton(PublisherManager::class, fn ($app) => new PublisherManager([
+            $app->make(WordPressPublisher::class),
+            $app->make(RedditPublisher::class),
+        ]));
     }
 
     /**