Fix critical OAuth MCP foundation issues

[prvnsmpth]

Summary

Stacked on #377. Merge this immediately after #377; until then GitHub will show the foundation commits in this PR as well.

• restore Rust compilation by initializing optional action scope metadata in the remaining connector-manager and Google action definitions
• bound OAuth refresh requests so a stalled provider cannot hold a database transaction indefinitely
• make MCP catalog discovery atomic and clear stale cached catalogs when OAuth-backed discovery fails
• buffer empty provider envelopes so the one-time recovery retry does not emit or persist a duplicate assistant response

The intentionally deferred cross-SDK action-scope metadata abstraction is not addressed here.

Validation

• cargo check -p omni-connector-manager -p omni-google-connector -p omni-connector-sdk
• cargo test -p shared oauth_refresh_tests
• cargo test -p omni-indexer test_completed_sync_is_ready_below_batch_threshold
• cd sdk/typescript && npm test (86 tests)
• cd sdk/typescript && npm run build
• Python files compile successfully with python3 -m compileall; the AI test environment dependencies are not installed locally