fix: scree plot uses party vectors instead of individual MPs

current_parliament has two separate SVD data spaces mixed together.
Party vectors (entity_id without comma) carry the between-party signal
in dims 0-15. Individual MP vectors only have signal in dim 3 and
dims 16-49 (within-party variance). The axis chart uses party vectors,
so the scree must too.

explorer.py

@@ -262,27 +262,27 @@ def load_party_axis_scores(db_path: str) -> Dict[str, List[float]]:
 
 @st.cache_data(show_spinner="Scree-plot laden…")
 def load_scree_data(db_path: str) -> List[float]:
-    """Return component importances (L2-norm per SVD dimension), sorted descending.
+    """Return party-level component importances (L2-norm per SVD dim), sorted descending.
 
-    Uses ALL individual MP vectors (entity_type='mp', window='current_parliament'),
+    The current_parliament window contains two separate SVD data spaces:
-    excluding party-aggregated rows. Since the stored vectors are U*s (scaled by
+    - Party vectors (entity_id without comma): dims 0–15 have political signal
-    singular values), the L2-norm of all MP scores per dimension approximates the
+    - Individual MP vectors (entity_id with comma): signal in dim 3 + dims 16–49
-    singular value for that dimension. Sorting descending gives the proper scree shape.
+      (within-party variance, unrelated to between-party differences)
 
-    Note: Procrustes alignment across sub-windows may scramble the original dimension
+    Since the SVD tab axis chart uses party vectors exclusively, the scree plot
-    ordering, so we sort by magnitude rather than relying on dimension index order.
+    must also use party vectors. We filter to entries with L2-norm > 1 (excludes
+    near-empty/historical party entries), compute L2-norm per dim, then sort
+    descending so the elbow shape is visible.
     """
     try:
         con = duckdb.connect(database=db_path, read_only=True)
         rows = con.execute(
             "SELECT entity_id, vector FROM svd_vectors "
-            "WHERE entity_type='mp' AND window_id='current_parliament'"
+            "WHERE entity_type='mp' AND window_id='current_parliament' "
+            "AND entity_id NOT LIKE '%,%'"
         ).fetchall()
-        # Individual MPs have "Lastname, F." format; party rows are short codes without commas
         vectors: List[List[float]] = []
         for entity_id, raw_vec in rows:
-            if "," not in entity_id:
-                continue  # skip party-aggregated rows
             if isinstance(raw_vec, str):
                 vec = json.loads(raw_vec)
             elif isinstance(raw_vec, (bytes, bytearray)):
@@ -294,7 +294,10 @@ def load_scree_data(db_path: str) -> List[float]:
                     vec = list(raw_vec)
                 except Exception:
                     continue
-            vectors.append([float(v) if v is not None else 0.0 for v in vec])
+            fvec = [float(v) if v is not None else 0.0 for v in vec]
+            l2 = sum(x**2 for x in fvec) ** 0.5
+            if l2 > 1.0:  # skip near-empty / historical party entries
+                vectors.append(fvec)
         if not vectors:
             return []
         n_dims = len(vectors[0])