feat(pipeline): implement parliamentary embedding pipeline MVP

- Add 4 migration files: mp_votes, mp_metadata, svd_vectors, fused_embeddings
- Extend database.py with 5 new helper methods and table init
- Add pipeline/ package: extract_mp_votes, fetch_mp_metadata, text_pipeline,
  svd_pipeline (with Procrustes alignment), fusion
- Add full test suite (17 tests) covering all pipeline modules and migrations
- Fix Procrustes alignment bug: scipy scale is a norm value, not a multiplier
- Fix DuckDB date type handling in test assertions (datetime.date vs string)
- Remove duckdb.py shim; tests now run against real duckdb + scipy via uv

Ref: thoughts/shared/plans/2026-03-21-parliamentary-embedding-pipeline-plan.md

tests/types/test_motion_types.py

@@ -0,0 +1,22 @@
+import json
+
+from src.types.motion_types import SimilarityNeighbor, to_json, from_json
+
+
+def test_similarity_neighbor_json_roundtrip():
+    neighbors = [
+        SimilarityNeighbor(motion_id="m1", score=0.9),
+        SimilarityNeighbor(motion_id="m2", score=0.75),
+    ]
+
+    # Serialize to JSON string
+    json_str = to_json(neighbors)
+    assert isinstance(json_str, str)
+
+    # Ensure it's valid JSON
+    parsed = json.loads(json_str)
+    assert isinstance(parsed, list)
+
+    # Deserialize back to objects
+    recovered = from_json(json_str)
+    assert recovered == neighbors