feat(embedding): add API-only retrieve_chunks() semantic search

paperforge/embedding/search.py

@@ -0,0 +1,39 @@
+from __future__ import annotations
+
+import logging
+from pathlib import Path
+
+from paperforge.embedding._chroma import get_collection
+from paperforge.embedding.providers.openai_compatible import OpenAICompatibleProvider
+
+logger = logging.getLogger(__name__)
+
+
+def retrieve_chunks(vault: Path, query: str, limit: int = 5, expand: bool = True) -> list[dict]:
+    """Search chunks via API embedding. Returns list with metadata and similarity scores."""
+    collection = get_collection(vault)
+    provider = OpenAICompatibleProvider(vault)
+    query_embedding = provider.encode_single(query)
+
+    results = collection.query(
+        query_embeddings=[query_embedding],
+        n_results=limit * 3 if expand else limit,
+        include=["documents", "metadatas", "distances"],
+    )
+
+    chunks = []
+    for i, (doc, meta, dist) in enumerate(zip(
+        results["documents"][0],
+        results["metadatas"][0],
+        results["distances"][0],
+    )):
+        chunks.append({
+            "paper_id": meta["paper_id"],
+            "section": meta.get("section", "Text"),
+            "page_number": meta.get("page_number", 1),
+            "chunk_index": meta.get("chunk_index", 0),
+            "chunk_text": doc,
+            "score": round(1.0 - dist, 4),
+        })
+
+    return chunks