Fix PREVIEW_DIR so preview cleanup targets the served folder

PREVIEW_DIR pointed at Playground\Viewer\public\previews, but the app lives at
Playground\Apps\Viewer. The clear-on-workflow-start in styles_pipe has therefore been
sweeping an empty folder since the app moved, while real previews accumulated untouched
in the served one - 9 files / 4.26 MB found and removed.

Resolves against a candidate list now (RM_PREVIEW_DIR, current location, legacy), first
existing wins, so moving the app again cannot silently resurrect this.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Claude-Session: https://claude.ai/code/session_012uM7Ru1JYn48n6c5Rzwd99

nodes/progress_reporter.py

@@ -16,7 +16,28 @@ except ImportError:
     HAS_REQUESTS = False
 
 VIEWER_URL = "http://127.0.0.1:3001/api/comfy-progress"
-PREVIEW_DIR = r"C:\Users\rober\Playground\Viewer\public\previews"
+
+# The Viewer serves previews from <app>/public/previews. This pointed at
+# Playground\Viewer for a long time - the app actually lives at Playground\Apps\Viewer -
+# so the clear-on-workflow-start below was sweeping an empty folder while real previews
+# accumulated untouched in the served one. First existing candidate wins, so moving the
+# app again does not silently resurrect that.
+_PREVIEW_CANDIDATES = [
+    os.environ.get("RM_PREVIEW_DIR", ""),
+    r"C:\Users\rober\Playground\Apps\Viewer\public\previews",
+    r"C:\Users\rober\Playground\Viewer\public\previews",
+]
+
+
+def _resolve_preview_dir():
+    for candidate in _PREVIEW_CANDIDATES:
+        if candidate and os.path.isdir(candidate):
+            return candidate
+    # Nothing exists yet: prefer the current app location rather than the legacy one.
+    return _PREVIEW_CANDIDATES[1]
+
+
+PREVIEW_DIR = _resolve_preview_dir()
 
 
 def ensure_preview_dir():