Added a hook to handle AskUserQuestion

[riley-mete-db]

Summary

Adds a PreToolUse hook to block the AskUserQuestion tool in the headless Builder App agent, redirecting it to ask questions as plain text in the response instead of failing silently.

Files Modified

• databricks-builder-app/server/services/agent.py — New _create_ask_user_hook() factory that denies AskUserQuestion via PreToolUse hook with a system message redirecting the agent
  to ask via text; hook registered in _run_agent_in_fresh_loop() for all executions; ruff formatting fixes (single quotes, line wrapping, import sorting)
• databricks-builder-app/client/src/pages/ProjectPage.tsx — Minor refactor: extracted toolName variable in tool_use event handler to avoid duplicate casts

Test Plan

[x] Tested locally using ./scripts/setup.sh and ./scripts/start_dev.sh with my databricks workspace.
[x] Verified hook itercepts AskUserQuestion - agent asks via text instead of failing
[x] Verified agent continues normally after hook
[x] Verified agent executes normally when no AskUserQuestion is used

Screenshots

[calreynolds]

pausing this PR for now in favor of adding the claude-native skill to the approved tools!

[riley-mete-db]

When testing locally, the poller (Lemma) would sometimes miss final events because the endpoint previously ignored completed streams, falling through to the DB before persist_loop had flushed them. This change falls back to the most recently completed in-memory stream (which lingers for 5 minutes before cleanup), giving the poller time to drain all events. It doesn't affect the stream itself, just adds robustness to polling.

This race condition mostly surfaces locally where slower calls widen the timing window, but can still occur in prod under load.