fix(chunk-context): address PR #767 review — doc_type filter parity + tests

- Add `doc_type` FieldCondition to the chunk_index-path highlighted-image
  Qdrant filter in both `api/visualization.py` and `auth/viz_routes.py`,
  matching the shape of `_get_chunk_by_index_from_qdrant`. Safe today (the
  block is guarded by `doc_type == "file"` and Nextcloud file IDs are
  globally unique) but prevents a latent bug if other doc types start
  storing highlighted images.
- Demote `viz_routes.py` `ValueError` log from `error` to `warning` (lazy
  %-style) — `_parse_int_param` raises on user-supplied bad input, which
  is a 400 not a server error and shouldn't pollute error logs.
- Hoist `effective_chunk_index` to compute once at the top of
  `get_chunk_with_context`, removing two duplicate assignments.
- Add `test_file_doc_type_qdrant_miss_yields_fast_404` to the management
  endpoint tests, locking in the proxy-timeout fix contract.
- Add `tests/unit/test_viz_routes_chunk_context.py` mirroring management
  coverage for the OAuth-session route: param forwarding (chunk_index /
  total_chunks), `doc_type=file` fast 404, and 400 on invalid int params.

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

nextcloud_mcp_server/api/visualization.py

@@ -592,6 +592,10 @@ async def get_chunk_context(request: Request) -> JSONResponse:
                                 FieldCondition(
                                     key="user_id", match=MatchValue(value=user_id)
                                 ),
+                                FieldCondition(
+                                    key="doc_type",
+                                    match=MatchValue(value=doc_type),
+                                ),
                                 chunk_filter,
                             ]
                         ),