Make the timed-out salvage test outlast the launch it races

[ppXD]

Summary

• AgentBranchPushFlowTests.P2_2_a_timed_out_run_salvages_its_real_edit_as_a_real_pushed_branch gave its run a 1s wall deadline. That deadline is armed when the launch is bound (LocalProcessRunner.NativeLaunch.cs:76), before the runner host's broker, exec bootstrap and guardian processes start and before /bin/sh runs. On a loaded host the launch alone took 1.0–2.0s, so the kill sometimes landed before the agent's write. The test then failed with an empty ChangedFiles, which looked like broken salvage even though salvage never ran.
• The deadline is now 10s. The script runs printf ... > salvaged.txt && echo written; sleep 300, and the test reads written back through the run's recorded events (IAgentRunService.GetEventsAsync) before it checks the capture. If a launch ever overruns the deadline, the failure says so instead of blaming salvage. Everything the test proves is unchanged: the run ends TimedOut, the file is in ChangedFiles, and the branch is really pushed to the bare remote and contains the file.
• Only the test file changes.

Test plan

• Reproduced the CI failure with the original test under 10x CPU oversubscription (120 busy loops on 12 cores): 3 of 6 runs red with ChangedFiles ... but was actually []
• Fixed test, idle: 20/20 green
• Fixed test, same 10x oversubscription: 20/20 green
• Mutation: remove TimedOut from the salvage push gate in PushProducedBranchIfEnabledAsync → red at ProducedBranch
• Mutation: skip EnrichWithWorkspaceChangesAsync for TimedOut → red at ChangedFiles, after the written precondition passes
• Mutation: delay the agent's write past the deadline → red at the written precondition, with a message that names the launch overrun
• AgentBranchPushFlowTests class: 4/4 green
• CI integration lane green