Allow searching runs by run parameters

[marciok]

Summary

Add server-side search to the runs listing so users can find runs using values stored in their run parameters.

Acceptance criteria

• The runs listing includes a clearly labeled parameter search control.
• Searching returns only runs for the current DAG whose parameter keys or values match the query.
• Parameter search works together with the existing status filter and pagination.
• Clearing the search restores the unfiltered run list.
• The active search is represented in the URL so it survives refreshes and pagination changes.
• Matching is performed server-side without loading all runs into the LiveView.
• Add context and LiveView tests covering matches, no matches, clearing, status combinations, and pagination.