feat(deployments): support Docker image tags for preview deployments

Add end-to-end support for `docker_registry_image_tag` in preview and deployment queue flows.

- Extend deploy API to accept `pull_request_id` alias and `docker_tag` for preview deploys
- Persist preview-specific Docker tags on `application_previews` and `application_deployment_queues`
- Pass tag through `queue_application_deployment()` and de-duplicate queued jobs by tag
- Update deployment job logic to resolve and use preview Docker tags for dockerimage build packs
- Update Livewire previews UI/state to manage per-preview tags and manual preview/tag inputs
- Add migration for new tag columns and model fillable/casts updates
- Add feature and unit tests covering API behavior and tag resolution

database/migrations/2026_03_30_120000_add_docker_registry_image_tag_to_application_previews_and_deployment_queues.php

@@ -0,0 +1,30 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::table('application_previews', function (Blueprint $table) {
+            $table->string('docker_registry_image_tag')->nullable()->after('docker_compose_domains');
+        });
+
+        Schema::table('application_deployment_queues', function (Blueprint $table) {
+            $table->string('docker_registry_image_tag')->nullable()->after('pull_request_id');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('application_previews', function (Blueprint $table) {
+            $table->dropColumn('docker_registry_image_tag');
+        });
+
+        Schema::table('application_deployment_queues', function (Blueprint $table) {
+            $table->dropColumn('docker_registry_image_tag');
+        });
+    }
+};