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/Http/Resources/PostResource.php

@@ -16,9 +16,11 @@ class PostResource extends JsonResource
             'type' => $this->type,
             'title' => $this->title,
             'body' => $this->body,
+            'target' => $this->target,
             'status' => $this->status,
             'scheduled_at' => $this->scheduled_at,
             'published_url' => $this->published_url,
+            'publish_error' => $this->publish_error,
             'created_at' => $this->created_at,
             'updated_at' => $this->updated_at,
         ];