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>

database/migrations/2026_07_21_133845_add_publishing_fields_to_posts_table.php

@@ -0,0 +1,35 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('posts', function (Blueprint $table) {
+            $table->string('target')->nullable()->after('body');
+            $table->text('publish_error')->nullable()->after('published_url');
+        });
+
+        DB::statement("ALTER TABLE posts MODIFY status ENUM('draft', 'scheduled', 'publishing', 'published', 'failed') NOT NULL DEFAULT 'draft'");
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        DB::statement("UPDATE posts SET status = 'failed' WHERE status = 'publishing'");
+        DB::statement("ALTER TABLE posts MODIFY status ENUM('draft', 'scheduled', 'published', 'failed') NOT NULL DEFAULT 'draft'");
+
+        Schema::table('posts', function (Blueprint $table) {
+            $table->dropColumn(['target', 'publish_error']);
+        });
+    }
+};