[P2.2] Offload synchronous SQLite calls in async task/costs handlers

[frankbria]

Severity: medium | Category: infra | Phase: P2.2

Problem

async def handlers call blocking sqlite directly, serializing concurrent requests behind disk I/O on the event-loop thread.

Evidence

codeframe/ui/routers/tasks_v2.py:237, codeframe/ui/routers/costs_v2.py:298

Acceptance criteria

DB work offloaded via asyncio.to_thread, or handlers declared plain def.

Dependencies

blocked by #732 ([P1.5])

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_{Filed from the SaaS launch-readiness audit. Atomic: one developer, one session. Work order: strictly P0.1 → P3.12 (no forward dependencies).}

[coderabbitai]

🔗 Related PRs

#686 - fix(core): add busy_timeout + WAL to workspace SQLite connections (#648) [closed]

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