fix(rag): strip HTML tags before chunking + D5 re-ingestion scripts

HTML files from gesetze-im-internet.de were decoded as raw UTF-8, keeping
<div>/<p> tags intact. The legal chunker regex requires § at line start,
which never matched inside HTML tags → 0% section metadata for HTML docs.

Fix: detect HTML content and strip tags before sending to embedding
service. Block elements become newlines, entities are decoded.
§ signs now appear at line starts → section detection works.

Also adds D5 re-ingestion scripts (reingest_d5.py + config) for
batch re-processing of all documents in Qdrant collections.

27 rag-service tests passing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

rag-service/api/documents.py

@@ -7,6 +7,7 @@ from pydantic import BaseModel
 
 from api.auth import optional_jwt_auth
 from embedding_client import embedding_client
+from html_utils import looks_like_html, strip_html
 from minio_client_wrapper import minio_wrapper
 from qdrant_client_wrapper import qdrant_wrapper
 
@@ -111,6 +112,11 @@ async def upload_document(
     if not text or not text.strip():
         raise HTTPException(status_code=400, detail="Could not extract any text from the document")
 
+    # --- Strip HTML if detected ---
+    if looks_like_html(text):
+        text = strip_html(text)
+        logger.info("Stripped HTML tags from %s", filename)
+
     # --- Chunk ---
     try:
         chunk_result = await embedding_client.chunk_text(