fix: Preserve session state on idle-kill instead of destroying it

[charlesvien]

Problem

Idle killed sessions had their state fully torn down, preventing users from retrying with context intact.

Changes

1. Add handleIdleKill that marks sessions as errored without clearing events, logUrl or adapter
2. Guard idle kill against sessions with in-flight MCP tool calls
3. Include inFlightMcpToolCalls in hasActiveSessions check to prevent premature app quit
4. Add tests for idle kill behavior with non-empty and empty MCP tool call maps

How did you test this?

Manually

[charlesvien]

• feat: Add release notification workflow #1457
• fix: Preserve session state on idle-kill instead of destroying it #1459 👈 (View in Graphite)
• main

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