feat: add .zip document support and auto-mount cache dirs into remote backends (#4846)

- Add .zip to SUPPORTED_DOCUMENT_TYPES so gateway platforms (Telegram,
  Slack, Discord) cache uploaded zip files instead of rejecting them.
- Add get_cache_directory_mounts() and iter_cache_files() to
  credential_files.py for host-side cache directory passthrough
  (documents, images, audio, screenshots).
- Docker: bind-mount cache dirs read-only alongside credentials/skills.
  Changes are live (bind mount semantics).
- Modal: mount cache files at sandbox creation + resync before each
  command via _sync_files() with mtime+size change detection.
- Handles backward-compat with legacy dir names (document_cache,
  image_cache, audio_cache, browser_screenshots) via get_hermes_dir().
- Container paths always use the new cache/<subdir> layout regardless
  of host layout.

This replaces the need for a dedicated extract_archive tool (PR #4819)
— the agent can now use standard terminal commands (unzip, tar) on
uploaded files inside remote containers.

Closes: related to PR #4819 by kshitijk4poor

tests/gateway/test_telegram_documents.py

@@ -236,15 +236,16 @@ class TestDocumentDownloadBlock:
         assert "Please summarize" in event.text
 
     @pytest.mark.asyncio
-    async def test_unsupported_type_rejected(self, adapter):
+    async def test_zip_document_cached(self, adapter):
+        """A .zip upload should be cached as a supported document."""
         doc = _make_document(file_name="archive.zip", mime_type="application/zip", file_size=100)
         msg = _make_message(document=doc)
         update = _make_update(msg)
 
         await adapter._handle_media_message(update, MagicMock())
         event = adapter.handle_message.call_args[0][0]
-        assert "Unsupported document type" in event.text
-        assert ".zip" in event.text
+        assert event.media_urls and event.media_urls[0].endswith("archive.zip")
+        assert event.media_types == ["application/zip"]
 
     @pytest.mark.asyncio
     async def test_oversized_file_rejected(self, adapter):