feat(qdrant): add tenant-scoped point storage for ingestion

Why:
- Ingested chunks need to become searchable Qdrant points before the upload
  response returns, with tenant/domain isolation and a safe re-ingestion
  story per ADR-0001/0017.

Changes:
- src/application/points/: index_chunks() is the sole entry point, owning
  payload construction, batched/bounded-concurrency upserts
  (upsert_concurrency semaphore), and a soft-delete sweep for points a
  shorter re-ingestion leaves behind. The sweep runs only after every upsert
  in the attempt succeeds, so a failed attempt can leave a stale prefix but
  never removes content from a working index.
- PointStorage port (application/ports/) + QdrantPointStorage adapter
  (infrastructure/qdrant/points.py), keeping the qdrant_client SDK out of
  application code per ADR-0015.
- FakePointStorage test double for exercising the ordering/idempotency
  guarantees without a real Qdrant.

src/application/ports/point_storage.py

@@ -0,0 +1,45 @@
+"""The point-storage port (ADR-0001, ADR-0015).
+
+`src/infrastructure/qdrant/points.py` is the production adapter; tests use a
+hand-written fake (ADR-0016). Application code depends on this Protocol, not on
+the `qdrant_client` SDK.
+
+Deliberately narrow: exactly the two operations ingestion performs. Reads,
+single-point edits, reordering, and keyword search are plan 002's `/v1/points`
+surface and belong on a port of their own rather than accreting here.
+"""
+
+import uuid
+from collections.abc import Sequence
+from datetime import datetime
+from typing import Protocol
+
+from src.application.points.models import ChunkPoint
+
+
+class PointStorage(Protocol):
+    async def upsert_points(self, points: Sequence[ChunkPoint]) -> None:
+        """Upsert one batch of points.
+
+        Callers own batching and concurrency bounding (ADR-0017's
+        `upsert_concurrency` semaphore), not this Protocol — the same division
+        `DenseEmbedder.embed_batch` uses.
+        """
+        ...
+
+    async def deactivate_points_from_index(
+        self,
+        *,
+        tenant_id: uuid.UUID,
+        file_id: uuid.UUID,
+        from_chunk_index: int,
+        deleted_at: datetime,
+        updated_by: str,
+    ) -> int:
+        """Soft-delete this file's points at or past `from_chunk_index`.
+
+        Sets `is_active=false`/`deleted_at` rather than removing the points
+        (ADR-0002: delete is soft by default). Tenant-filtered — a `file_id`
+        alone is never sufficient authority. Returns how many points matched.
+        """
+        ...