* perf: fix database query performance bottlenecks
- Add composite index on workspace_repos(workspace_id, repo_id) to optimize lookup queries that were taking up to 5 seconds
- Add composite index on merges(merge_type, pr_status) to optimize status filtering queries that were taking 2+ seconds
- Fix N+1 query pattern in workspace_repos.create_many by wrapping inserts in a transaction
- Fix N+1 query pattern in get_task_attempt_branch_status by batch fetching all merges upfront instead of querying per repo
These changes address significant performance bottlenecks identified in production logs where simple lookup queries were experiencing multi-second latencies.
* cargo fmt
* run sqlx prepare
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Co-authored-by: Solomon <abcpro11051@disroot.org>
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