feat: flatten output into variants/ and intermediates/

Drop per-job subdirs for phone-friendly Syncthing layout with
stem-suffixed filenames; keep web state in meta/.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/remix.py

@@ -26,11 +26,12 @@ def build_remix_options(assets: FilterAssets) -> dict[str, list[str]]:
     }
 
 
-def create_remix_variant(job_id: str, original_suffix: str, choice: RemixChoice) -> dict:
+def create_remix_variant(job_id: str, choice: RemixChoice) -> dict:
     """Compose exactly one variant from explicit choices and append it to
-    the job's manifest. Raises PipelineError on failure (caller should show
+    the job's meta. Raises PipelineError on failure (caller should show
     it to the user, no half-written manifest entries are ever created)."""
-    paths: JobPaths = pipeline.job_paths(job_id, original_suffix)
+    stem = pipeline.sanitize_stem(job_id)
+    paths: JobPaths = pipeline.job_paths(stem, ".jpg")
     if not paths.original.exists() or not paths.rembg.exists():
         raise PipelineError("Original oder Rembg-Bild fehlt fuer diesen Job — Remix nicht moeglich.")
 
@@ -42,10 +43,11 @@ def create_remix_variant(job_id: str, original_suffix: str, choice: RemixChoice)
     if choice.bg_blend not in assets.blend_modes or choice.fg_blend not in assets.blend_modes:
         raise PipelineError("Unbekannter Blend-Modus.")
 
-    manifest = pipeline.read_manifest(job_id) or {
-        "job_id": job_id,
+    manifest = pipeline.read_manifest(stem) or {
+        "job_id": stem,
         "original_file": paths.original.name,
         "rembg_file": paths.rembg.name,
+        "source_stem": stem,
         "created_at": pipeline.now_iso(),
         "variants": [],
     }