fix(vector): address PR review round 2 — status branching, doc_id guard, doc restore

- _ensure_keyword_payload_indexes: distinguish 400 (schema conflict, warning)
  from other status codes (5xx/network, error) so a transient outage doesn't
  silently leave the collection unindexed.
- build_search_result_from_point: use .get("doc_id") + return None on missing
  instead of KeyError-crashing the search; reverse metadata merge order so
  payload-derived chunk_index/total_chunks win over caller-supplied extras.
- docs/configuration.md: restore the OpenAI/Mistral/Bedrock/Simple provider
  sections + reference-table rows that were dropped in the rebase. Reword
  the "Startup migrations" bullet to describe what the code actually does
  (no sampling — full scroll, zero writes when clean). Add operator note
  about the SemanticSearchResult.id TypeError path.
- tests: pytest.approx for float equality (Sonar python:S1244); coverage
  for non-400 → ERROR, payload={doc_id: None}, and missing doc_id key.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/vector/qdrant_client.py

@@ -46,9 +46,21 @@ async def _ensure_keyword_payload_indexes(
         except UnexpectedResponse as e:
             body = getattr(e, "content", b"") or b""
             body_text = body.decode("utf-8", errors="replace")
-            logger.warning(
-                "Failed to create payload index on '%s': %s", field, body_text
-            )
+            # 400 is the expected schema-conflict path (index already exists
+            # with a different type). 5xx / network-shaped errors should not
+            # be silently downgraded — keep the loop going so the remaining
+            # fields still get attempted, but log at error so operators see it.
+            if e.status_code == 400:
+                logger.warning(
+                    "Schema conflict on payload index '%s': %s", field, body_text
+                )
+            else:
+                logger.error(
+                    "Unexpected error creating payload index on '%s' (status %s): %s",
+                    field,
+                    e.status_code,
+                    body_text,
+                )
 
 
 async def _backfill_doc_id_to_string(