feat: auto feature detection with filename prefixes on export

Detects QR codes (QR_), barcodes (BC_), faces (FACE_/GROUP_),
and panoramas (PANO_) per photo using OpenCV — no new dependencies.
Opt-in checkboxes in the rename tab; prefixes prepend to filename.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server.py

@@ -124,6 +124,7 @@ class ExportRequest(BaseModel):
     text_watermark: dict = Field(default_factory=dict)
     image_watermark_path: str = ""
     image_watermark_settings: dict = Field(default_factory=dict)
+    feature_detectors: List[str] = Field(default_factory=list)
 
 
 @app.get("/")
@@ -400,6 +401,7 @@ def _run_export_job(job_id: str, req: ExportRequest):
         buf = io.BytesIO()
         used_names: set = set()
 
+        detectors = set(req.feature_detectors)
         with zipfile.ZipFile(buf, "w", zipfile.ZIP_DEFLATED) as zf:
             for i, path in enumerate(export_paths):
                 exif = get_exif_info(path)
@@ -407,6 +409,11 @@ def _run_export_job(job_id: str, req: ExportRequest):
                     path, req.rename_mode, req.rename_prefix,
                     i + 1, exif, path in fav_set, req.fav_prefix,
                 )
+                if detectors:
+                    from processor import detect_features
+                    feat_prefix = "".join(detect_features(path, detectors))
+                    if feat_prefix:
+                        new_name = feat_prefix + new_name
                 # Deduplicate filenames
                 base, ext = os.path.splitext(new_name)
                 candidate, n = new_name, 1