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_document_cache.py

@@ -151,7 +151,7 @@ class TestSupportedDocumentTypes:
 
     @pytest.mark.parametrize(
         "ext",
-        [".pdf", ".md", ".txt", ".docx", ".xlsx", ".pptx"],
+        [".pdf", ".md", ".txt", ".zip", ".docx", ".xlsx", ".pptx"],
     )
     def test_expected_extensions_present(self, ext):
         assert ext in SUPPORTED_DOCUMENT_TYPES