refactor: wire all services through ApplicationContext

- Created src/application_context.py as DI container with TYPE_CHECKING imports
- server.py now instantiates all services in dependency order via ApplicationContext
- Fixed infinite recursion bug: 48 instance methods renamed with underscore prefix
  to avoid shadowing by same-named @classmethod forwarders
- ZeroconfServer: instantiate Zeroconf() in __init__, add _sync_class() to
  configure forwarder, direct _configure/_start calls during wiring
- Config, EngineManager, PreviewManager: all forwarders and _sync_class() intact
- RenderQueue: load_state and subscribe moved to __init__, threading.Lock retained
- DistributedJobManager: subscribe_to_listener moved to __init__

src/api/preview_manager.py

@@ -3,6 +3,7 @@ import os
 import subprocess
 import threading
 from pathlib import Path
+from typing import Dict, Optional
 
 from src.utilities.ffmpeg_helper import generate_thumbnail, save_first_frame
 
@@ -12,12 +13,20 @@ supported_image_formats = ['.jpg', '.png', '.exr', '.tif', '.tga', '.bmp', '.web
 
 
 class PreviewManager:
+    _default_instance: Optional['PreviewManager'] = None
 
-    storage_path = None
-    _running_jobs = {}
+    storage_path: Optional[str] = None
+
+    def __init__(self) -> None:
+        self.storage_path = None
+        self._running_jobs: Dict = {}
 
     @classmethod
-    def __generate_job_preview_worker(cls, job, replace_existing=False, max_width=480):
+    def _sync_class(cls) -> None:
+        if cls._default_instance is not None:
+            cls.storage_path = cls._default_instance.storage_path
+
+    def _generate_job_preview_worker(self, job, replace_existing=False, max_width=480):
 
         # Determine best source file to use for thumbs
         job_file_list = job.file_list()
@@ -33,8 +42,8 @@ class PreviewManager:
             logger.warning(f"No valid image or video files found in files from job: {job}")
             return
 
-        os.makedirs(cls.storage_path, exist_ok=True)
-        base_path = os.path.join(cls.storage_path, f"{job.id}-{preview_label}-{max_width}")
+        os.makedirs(self.storage_path, exist_ok=True)
+        base_path = os.path.join(self.storage_path, f"{job.id}-{preview_label}-{max_width}")
         preview_video_path = base_path + '.mp4'
         preview_image_path = base_path + '.jpg'
 
@@ -65,25 +74,23 @@ class PreviewManager:
             except subprocess.CalledProcessError as e:
                 logger.error(f"Error generating video preview for {job}: {e}")
 
-    @classmethod
-    def update_previews_for_job(cls, job, replace_existing=False, wait_until_completion=False, timeout=None):
-        job_thread = cls._running_jobs.get(job.id)
+    def _update_previews_for_job(self, job, replace_existing=False, wait_until_completion=False, timeout=None):
+        job_thread = self._running_jobs.get(job.id)
         if job_thread and job_thread.is_alive():
             logger.debug(f'Preview generation job already running for {job}')
         else:
-            job_thread = threading.Thread(target=cls.__generate_job_preview_worker, args=(job, replace_existing,))
+            job_thread = threading.Thread(target=self._generate_job_preview_worker, args=(job, replace_existing,))
             job_thread.start()
-            cls._running_jobs[job.id] = job_thread
+            self._running_jobs[job.id] = job_thread
 
         if wait_until_completion:
             job_thread.join(timeout=timeout)
 
-    @classmethod
-    def get_previews_for_job(cls, job):
+    def _get_previews_for_job(self, job):
 
         results = {}
         try:
-            directory_path = Path(cls.storage_path)
+            directory_path = Path(self.storage_path)
             preview_files_for_job = [f for f in directory_path.iterdir() if f.is_file() and f.name.startswith(job.id)]
 
             for preview_filename in preview_files_for_job:
@@ -101,9 +108,8 @@ class PreviewManager:
             pass
         return results
 
-    @classmethod
-    def delete_previews_for_job(cls, job):
-        all_previews = cls.get_previews_for_job(job)
+    def _delete_previews_for_job(self, job):
+        all_previews = self.get_previews_for_job(job)
         flattened_list = [item for sublist in all_previews.values() for item in sublist]
         for preview in flattened_list:
             try:
@@ -111,3 +117,21 @@ class PreviewManager:
                 os.remove(preview['filename'])
             except OSError as e:
                 logger.error(f"Error removing preview '{preview.get('filename')}': {e}")
+
+    # --- Forwarders for backward compatibility ---
+
+    @classmethod
+    def update_previews_for_job(cls, job, replace_existing=False, wait_until_completion=False, timeout=None):
+        if cls._default_instance is not None:
+            cls._default_instance._update_previews_for_job(job, replace_existing, wait_until_completion, timeout)
+
+    @classmethod
+    def get_previews_for_job(cls, job):
+        if cls._default_instance is not None:
+            return cls._default_instance._get_previews_for_job(job)
+        return {}
+
+    @classmethod
+    def delete_previews_for_job(cls, job):
+        if cls._default_instance is not None:
+            cls._default_instance._delete_previews_for_job(job)