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/Support/Publishing/PublisherManager.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace App\Support\Publishing;
+
+use App\Models\Post;
+
+class PublisherManager
+{
+    /**
+     * @param  array<Publisher>  $publishers
+     */
+    public function __construct(private readonly array $publishers) {}
+
+    public function resolve(Post $post): ?Publisher
+    {
+        foreach ($this->publishers as $publisher) {
+            if ($publisher->supports($post)) {
+                return $publisher;
+            }
+        }
+
+        return null;
+    }
+}