Add script/TTS step handlers, dashboard, and pipeline UI (#35, #36, #43, #44)

StepHandler abstraction (app/Support/VideoWorkflow/StepHandlers/) plugs
into WorkflowEngine without coupling it to how any given step type is
actually executed:
- ScriptGenerationHandler: builds a prompt from the project's title/
  description (or an explicit outline/tone/keywords/target length in
  step input), generates via an active OpenAI AiProvider, stores the
  result as a 'script' asset.
- TtsVoiceoverHandler: voices step.input.text, or falls back to the
  project's latest script asset, via an active ElevenLabs AiProvider;
  voice_id/model_id are configurable per step. No direct "speed"
  control — ElevenLabs' base TTS endpoint doesn't expose one.

RunWorkflowStepJob resolves a step's handler by type and runs it on
the queue, matching the existing PublishPostJob pattern (including a
stale-dispatch guard: no-op if the step isn't 'in_progress' anymore).

UI, under its own /video-projects routes and nav entry — separate
from /projects per the earlier decision:
- VideoProjects/Index (#43): list projects with status and step
  progress, create new ones.
- VideoProjects/Show (#44): start a project from a WorkflowTemplate or
  a hardcoded default 8-step pipeline; per-step Run/Approve/Reject/
  Retry/Skip actions; auto-queues the next step after any transition
  when a handler exists for its type (steps with no handler yet just
  sit in_progress rather than auto-failing); lists project assets.

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

app/Providers/AppServiceProvider.php

@@ -11,6 +11,9 @@ use App\Support\Publishing\PublisherManager;
 use App\Support\Publishing\RedditPublisher;
 use App\Support\Publishing\TwitterPublisher;
 use App\Support\Publishing\WordPressPublisher;
+use App\Support\VideoWorkflow\StepHandlers\ScriptGenerationHandler;
+use App\Support\VideoWorkflow\StepHandlers\StepHandlerManager;
+use App\Support\VideoWorkflow\StepHandlers\TtsVoiceoverHandler;
 use Illuminate\Support\ServiceProvider;
 
 class AppServiceProvider extends ServiceProvider
@@ -32,6 +35,11 @@ class AppServiceProvider extends ServiceProvider
             'stability_ai' => $app->make(StabilityAiDriver::class),
             'elevenlabs' => $app->make(ElevenLabsDriver::class),
         ]));
+
+        $this->app->singleton(StepHandlerManager::class, fn ($app) => new StepHandlerManager([
+            $app->make(ScriptGenerationHandler::class),
+            $app->make(TtsVoiceoverHandler::class),
+        ]));
     }
 
     /**