feat(ingestion): add bounded, benchmark-aligned embedding execution

Why:
- Plan 001 Phase 4 needs batched, concurrency-bounded embedding wired into
  the inline upload path, with process-wide capacity/timeout/chunk-limit
  guards (ADR-0017).
- The BM25 analyzer and dense-model config are ported from the `emet`
  evaluation lab, which benchmarked them against the real Farsi corpus
  (bm25-fa-norm-stop; nomic-embed-text-v2-moe at 768-dim; text-embedding-3-large
  at native 3072-dim), closing open items in ADR-0001/ADR-0005.

Changes:
- New: embedding ports, orchestration (embed_chunks), request-bounds
  helpers, and dense/sparse adapters (analyzers.py, bm25.py,
  openai_compatible.py).
- upload.py now parses/chunks/embeds inline behind INGESTION_MAX_CONCURRENCY
  (503), INGESTION_TIMEOUT_SECONDS (504), and the chunk-count ceiling (413);
  every failure path still writes a terminal job row.
- Lifespan builds and warms both dense embedders at startup (fail-soft) and
  creates the sparse embedder and concurrency semaphore.
- httpx moves from dev to main dependencies (adapters use it directly).

Impact:
- Qdrant point upserts are still Phase 5 -- chunks_indexed stays 0.
- New EMBEDDING_* env vars documented in .env.example; safe defaults.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/bootstrap/dependencies.py

@@ -1,12 +1,13 @@
-from collections.abc import AsyncIterator
+from collections.abc import AsyncIterator, Sequence
 from dataclasses import dataclass
 
-from anyio import CapacityLimiter
+from anyio import CapacityLimiter, Semaphore
 from fastapi import Request
 from minio import Minio
 from qdrant_client import AsyncQdrantClient
 from sqlalchemy.ext.asyncio import AsyncEngine, AsyncSession, async_sessionmaker
 
+from src.application.ports.embedding import DenseEmbedder, SparseEmbedder
 from src.application.ports.object_storage import ObjectStorage
 from src.config import Settings
 
@@ -20,6 +21,9 @@ class AppResources:
     qdrant_client: AsyncQdrantClient
     object_storage: ObjectStorage
     ingestion_limiter: CapacityLimiter
+    dense_embedders: Sequence[DenseEmbedder]
+    sparse_embedder: SparseEmbedder
+    ingestion_concurrency_limiter: Semaphore
 
 
 def _resources(request: Request) -> AppResources:
@@ -46,6 +50,18 @@ def get_ingestion_limiter(request: Request) -> CapacityLimiter:
     return _resources(request).ingestion_limiter
 
 
+def get_dense_embedders(request: Request) -> Sequence[DenseEmbedder]:
+    return _resources(request).dense_embedders
+
+
+def get_sparse_embedder(request: Request) -> SparseEmbedder:
+    return _resources(request).sparse_embedder
+
+
+def get_ingestion_concurrency_limiter(request: Request) -> Semaphore:
+    return _resources(request).ingestion_concurrency_limiter
+
+
 def get_sessionmaker(request: Request) -> async_sessionmaker[AsyncSession]:
     """The session *factory*, not a request-scoped session.