Add preview image handling for Civitai models and enhance job processing

- Introduced the `pick_preview_image` function to extract the first usable preview image URL and its suffix from model version data.
- Updated the `seed_civitai` function to include preview image URLs and destinations in job definitions, improving model handling.
- Implemented the `ensure_preview` function to download missing preview images during job processing, enhancing user experience.
- Added tests for `pick_preview_image` to ensure correct functionality across various scenarios, ensuring robustness in image handling.

src/gpu_rent/provision.py

@@ -11,7 +11,7 @@ from pathlib import Path
 
 import httpx
 
-from gpu_rent.civitai import fetch_model_version, pick_primary_file
+from gpu_rent.civitai import fetch_model_version, pick_preview_image, pick_primary_file
 from gpu_rent.config import Config
 from gpu_rent.errors import CloudError, GpuRentError
 from gpu_rent.manifests import (
@@ -126,6 +126,14 @@ def seed_extensions(cfg: Config, host: str, log: Log, *, update: bool = True) ->
         else:
             log("extensions.yaml пуст — стоковый SwarmUI")
         return False
+    if not repos and update:
+        if not all_repos:
+            log("extensions.yaml пуст — только update уже установленных на data (если есть)")
+        else:
+            log(
+                "extensions: yaml отфильтрован по requires "
+                f"(LLM_RUNTIME={runtime}) — только update установленных"
+            )
     jobs = []
     for repo in repos:
         jobs.append(
@@ -462,18 +470,22 @@ def seed_civitai(cfg: Config, host: str, log: Log) -> None:
             ),
             "tags": version.get("tags") or [],
         }
-        jobs.append(
-            {
-                "dest": dest,
-                "url": _download_url(api_host, vid, info),
-                "sha256": sha,
-                "auth": "civitai",
-                "sidecars": {
-                    f"{stem}.civitai.json": civitai_json,
-                    f"{stem}.swarm.json": json.dumps(swarm, ensure_ascii=False, indent=2),
-                },
-            }
-        )
+        job: dict = {
+            "dest": dest,
+            "url": _download_url(api_host, vid, info),
+            "sha256": sha,
+            "auth": "civitai",
+            "sidecars": {
+                f"{stem}.civitai.json": civitai_json,
+                f"{stem}.swarm.json": json.dumps(swarm, ensure_ascii=False, indent=2),
+            },
+        }
+        preview = pick_preview_image(version)
+        if preview:
+            preview_url, preview_suffix = preview
+            job["preview_url"] = preview_url
+            job["preview_dest"] = f"{DATA}/Models/{folder}/{stem}{preview_suffix}"
+        jobs.append(job)
 
     if not jobs:
         if not cfg.civitai_api_token: