feat(webapp,clickhouse): return an actionable error instead of a 500 when a runs list query is too expensive (#4773)

## Summary

When a runs list query is too expensive to complete, it now fails with a
clear, actionable error instead of a generic 500.

Previously, a runs list query that exceeded ClickHouse resource limits
threw an opaque error. On the public `runs.list` API that surfaced as a
retryable 500, so a customer task calling it would keep retrying a query
that could never succeed. On the dashboard it rendered as a generic
error page with no hint about what to do.

## Fix

The ClickHouse client now tags resource-limit failures (memory, time,
rows, bytes) with their error type, and the runs repository maps those
to a dedicated `RunsListQueryError` (HTTP 422).

- `runs.list` API returns 422 with a message telling the user to narrow
their `created_at` range, plus an `x-should-retry: false` header so the
SDK does not retry it.
- The dashboard runs list (and the errors, scheduled, standard-task,
agents, and webhooks list views) render a shared error state with the
same guidance, so a too-broad time filter is recoverable by the user.