feat(gateway): accept rar and 7z document uploads

[Qwinty]

Summary

• accept .rar and .7z as supported gateway document attachments
• keep archive uploads cached as documents so the agent can inspect them with existing terminal/file workflows
• add Telegram and shared document-cache regressions for the new archive types

Closes #28791.

Notes

This intentionally does not add archive extraction behavior or bundle extractor binaries. It only lets the gateway cache the uploaded archive and pass the local path to the agent, matching existing .zip behavior from #4846.

Test Plan

• RED: /usr/local/lib/hermes-agent/venv/bin/python -m pytest tests/gateway/test_document_cache.py::TestSupportedDocumentTypes::test_expected_extensions_present tests/gateway/test_telegram_documents.py::TestDocumentDownloadBlock::test_archive_document_cached -q failed for missing .rar/.7z
• GREEN: /usr/local/lib/hermes-agent/venv/bin/python -m pytest tests/gateway/test_document_cache.py::TestSupportedDocumentTypes::test_expected_extensions_present tests/gateway/test_telegram_documents.py::TestDocumentDownloadBlock::test_archive_document_cached -q
• /usr/local/lib/hermes-agent/venv/bin/python -m pytest tests/gateway/test_document_cache.py tests/gateway/test_telegram_documents.py -q
• git diff --check

[Qwinty]

CI note: all non-test checks are green on this PR. The test job hit the workflow-level 20-minute timeout and was cancelled, not a specific assertion failure.

This looks like existing CI behavior on current main rather than a regression from this small allowlist change: recent main Tests workflow runs are also cancelled after ~20 minutes (for example runs 26106201446 and 26099815519).

Local focused verification for this PR passed:

/usr/local/lib/hermes-agent/venv/bin/python -m pytest \
  tests/gateway/test_document_cache.py::TestSupportedDocumentTypes::test_expected_extensions_present \
  tests/gateway/test_telegram_documents.py::TestDocumentDownloadBlock::test_archive_document_cached \
  -q
# 11 passed

/usr/local/lib/hermes-agent/venv/bin/python -m pytest \
  tests/gateway/test_document_cache.py \
  tests/gateway/test_telegram_documents.py \
  -q
# 67 passed

[Qwinty]

Rebased on current upstream/main; PR is mergeable again.

Local verification:

• python -m pytest -q -o addopts='' tests/gateway/test_document_cache.py tests/gateway/test_telegram_documents.py - 67 passed
• python -m ruff check gateway/platforms/base.py tests/gateway/test_document_cache.py tests/gateway/test_telegram_documents.py - passed
• git diff --check upstream/main...HEAD - passed

CI has been retriggered on be6e259df.

[Qwinty]

Closing this optional/non-critical upstream feature PR to keep the open queue focused on production bugfixes. The branch can be reopened or recreated later if we decide to pursue this feature upstream.