feat(qdrant): provision the chunks collection as an explicit deployment step

Why:
- The chunks collection needs four named vectors (dense_nomic, dense_openai,
  sparse, late_interaction) and payload indexes defined at creation time per
  ADR-0001; sparse/multivector fields cannot be added to an existing
  collection without recreating it, so schema drift here is expensive.
- Creating it at FastAPI startup would mirror the DDL-at-boot anti-pattern
  ADR-0009 already rejects for Postgres and ADR-0012 rejects for LangGraph's
  setup(), so it is a deployment step instead.

Changes:
- src/infrastructure/qdrant/collection.py: ensure_chunks_collection(),
  idempotent and schema-verifying (raises on dimension/modifier mismatch
  rather than silently accepting a misconfigured collection).
- src/cli/qdrant_bootstrap.py: the operator entry point
  (python -m src.cli.qdrant_bootstrap).
- QdrantSettings gains collection/upsert_batch_size/upsert_concurrency.

Impact:
- Deployments must run the new bootstrap command before the first upload;
  see ADR-0001's new "Collection provisioning" section.

tests/integration/qdrant/test_collection.py

@@ -0,0 +1,114 @@
+"""`ensure_chunks_collection` against a real Qdrant (ADR-0001).
+
+The assertions that matter most here are the ones for schema properties that
+fail *silently* in production: the sparse `modifier=idf` and the pinned dense
+dimensions.
+"""
+
+import pytest
+from qdrant_client import AsyncQdrantClient, models
+
+from src.config import QdrantSettings
+from src.infrastructure.qdrant.collection import (
+    CollectionSchemaMismatchError,
+    ensure_chunks_collection,
+)
+
+pytestmark = [
+    pytest.mark.integration,
+    pytest.mark.qdrant,
+    pytest.mark.asyncio(loop_scope="session"),
+]
+
+
+async def test_ensure_chunks_collection_creates_all_four_named_vectors(
+    qdrant_client: AsyncQdrantClient, qdrant_settings: QdrantSettings
+) -> None:
+    created = await ensure_chunks_collection(qdrant_client, collection=qdrant_settings.collection)
+
+    assert created is True
+    info = await qdrant_client.get_collection(qdrant_settings.collection)
+    vectors = info.config.params.vectors
+    assert isinstance(vectors, dict)
+    assert vectors["dense_nomic"].size == 768
+    assert vectors["dense_openai"].size == 3072
+    assert vectors["late_interaction"].size == 128
+    assert vectors["late_interaction"].multivector_config is not None
+    assert vectors["late_interaction"].on_disk is True
+
+
+async def test_ensure_chunks_collection_sets_the_sparse_idf_modifier(
+    qdrant_client: AsyncQdrantClient, qdrant_settings: QdrantSettings
+) -> None:
+    """Without this, Qdrant applies no IDF and lexical retrieval silently
+    degrades -- no error, no warning (ADR-0005).
+    """
+    await ensure_chunks_collection(qdrant_client, collection=qdrant_settings.collection)
+
+    info = await qdrant_client.get_collection(qdrant_settings.collection)
+    sparse = info.config.params.sparse_vectors
+    assert sparse is not None
+    assert sparse["sparse"].modifier == models.Modifier.IDF
+
+
+async def test_ensure_chunks_collection_creates_the_payload_indexes(
+    qdrant_client: AsyncQdrantClient, qdrant_settings: QdrantSettings
+) -> None:
+    await ensure_chunks_collection(qdrant_client, collection=qdrant_settings.collection)
+
+    info = await qdrant_client.get_collection(qdrant_settings.collection)
+    schema = info.payload_schema
+    assert set(schema) >= {
+        "tenant_id",
+        "domain",
+        "file_id",
+        "order_id",
+        "previous_chunk_id",
+        "next_chunk_id",
+    }
+    # order_id must be numeric: Qdrant's Range/order_by reject keyword payloads.
+    assert schema["order_id"].data_type == models.PayloadSchemaType.FLOAT
+    assert schema["tenant_id"].data_type == models.PayloadSchemaType.KEYWORD
+
+
+async def test_ensure_chunks_collection_is_idempotent(
+    qdrant_client: AsyncQdrantClient, qdrant_settings: QdrantSettings
+) -> None:
+    assert await ensure_chunks_collection(qdrant_client, collection=qdrant_settings.collection)
+
+    assert not await ensure_chunks_collection(qdrant_client, collection=qdrant_settings.collection)
+
+
+async def test_ensure_chunks_collection_rejects_a_mismatched_existing_collection(
+    qdrant_client: AsyncQdrantClient, qdrant_settings: QdrantSettings
+) -> None:
+    """A wrong-dimension collection must fail loudly, not be silently accepted."""
+    await qdrant_client.create_collection(
+        collection_name=qdrant_settings.collection,
+        vectors_config={
+            "dense_nomic": models.VectorParams(size=384, distance=models.Distance.COSINE),
+            "dense_openai": models.VectorParams(size=3072, distance=models.Distance.COSINE),
+            "late_interaction": models.VectorParams(size=128, distance=models.Distance.COSINE),
+        },
+        sparse_vectors_config={"sparse": models.SparseVectorParams(modifier=models.Modifier.IDF)},
+    )
+
+    with pytest.raises(CollectionSchemaMismatchError, match="768"):
+        await ensure_chunks_collection(qdrant_client, collection=qdrant_settings.collection)
+
+
+async def test_ensure_chunks_collection_rejects_a_collection_without_the_idf_modifier(
+    qdrant_client: AsyncQdrantClient, qdrant_settings: QdrantSettings
+) -> None:
+    await qdrant_client.create_collection(
+        collection_name=qdrant_settings.collection,
+        vectors_config={
+            "dense_nomic": models.VectorParams(size=768, distance=models.Distance.COSINE),
+            "dense_openai": models.VectorParams(size=3072, distance=models.Distance.COSINE),
+            "late_interaction": models.VectorParams(size=128, distance=models.Distance.COSINE),
+        },
+        sparse_vectors_config={"sparse": models.SparseVectorParams()},
+    )
+
+    with pytest.raises(CollectionSchemaMismatchError, match="idf"):
+        await ensure_chunks_collection(qdrant_client, collection=qdrant_settings.collection)