feat: implement page limit estimation and enforcement in file based connector indexers

- Added a static method `estimate_pages_from_metadata` to `PageLimitService` for estimating page counts based on file metadata.
- Integrated page limit checks in Google Drive, Dropbox, and OneDrive indexers to prevent exceeding user quotas during file indexing.
- Updated relevant indexing methods to utilize the new page estimation logic and enforce limits accordingly.
- Enhanced tests for page limit functionality, ensuring accurate estimation and enforcement across different file types.

surfsense_backend/tests/integration/document_upload/conftest.py

@@ -3,6 +3,7 @@
 Prerequisites: PostgreSQL + pgvector only.
 
 External system boundaries are mocked:
+  - ETL parsing — LlamaParse (external API) and Docling (heavy library)
   - LLM summarization, text embedding, text chunking (external APIs)
   - Redis heartbeat (external infrastructure)
   - Task dispatch is swapped via DI (InlineTaskDispatcher)
@@ -11,6 +12,7 @@ External system boundaries are mocked:
 from __future__ import annotations
 
 import contextlib
+import os
 from collections.abc import AsyncGenerator
 from unittest.mock import AsyncMock, MagicMock
 
@@ -298,3 +300,64 @@ def _mock_redis_heartbeat(monkeypatch):
         "app.tasks.celery_tasks.document_tasks._run_heartbeat_loop",
         AsyncMock(),
     )
+
+
+@pytest.fixture(autouse=True)
+def _mock_etl_parsing(monkeypatch):
+    """Mock ETL parsing services — LlamaParse and Docling are external boundaries.
+
+    Preserves the real contract: empty/corrupt files raise an error just like
+    the actual services would, so tests covering failure paths keep working.
+    """
+
+    _MOCK_MARKDOWN = "# Mocked Document\n\nThis is mocked ETL content."
+
+    def _reject_empty(file_path: str) -> None:
+        if os.path.getsize(file_path) == 0:
+            raise RuntimeError(f"Cannot parse empty file: {file_path}")
+
+    # -- LlamaParse mock (external API) --------------------------------
+
+    class _FakeMarkdownDoc:
+        def __init__(self, text: str):
+            self.text = text
+
+    class _FakeLlamaParseResult:
+        async def aget_markdown_documents(self, *, split_by_page=False):
+            return [_FakeMarkdownDoc(_MOCK_MARKDOWN)]
+
+    async def _fake_llamacloud_parse(**kwargs):
+        _reject_empty(kwargs["file_path"])
+        return _FakeLlamaParseResult()
+
+    monkeypatch.setattr(
+        "app.tasks.document_processors.file_processors.parse_with_llamacloud_retry",
+        _fake_llamacloud_parse,
+    )
+
+    # -- Docling mock (heavy library boundary) -------------------------
+
+    async def _fake_docling_parse(file_path: str, filename: str):
+        _reject_empty(file_path)
+        return _MOCK_MARKDOWN
+
+    monkeypatch.setattr(
+        "app.tasks.document_processors.file_processors.parse_with_docling",
+        _fake_docling_parse,
+    )
+
+    class _FakeDoclingResult:
+        class document:
+            @staticmethod
+            def export_to_markdown():
+                return _MOCK_MARKDOWN
+
+    class _FakeDocumentConverter:
+        def convert(self, file_path):
+            _reject_empty(file_path)
+            return _FakeDoclingResult()
+
+    monkeypatch.setattr(
+        "docling.document_converter.DocumentConverter",
+        _FakeDocumentConverter,
+    )