fix(app-server): surface turn errors and process events

[gersmann]

Summary

• surface non-retryable turn error notifications as AppServerTurnError and deliver terminalInteraction events on turn streams
• add typed event subscriptions for command/exec output and process output/exit notifications keyed by process id/handle
• cover retryable errors, non-retryable errors, terminalInteraction delivery, and process event filters

Verification

• uv run --group dev pytest tests/test_app_server_client.py tests/test_app_server_async_client.py tests/test_stream_interaction.py -q
• make lint
• git diff --check

[github-actions]

Codex Autonomous Review:

• Overall: patch is correct
• New findings this run: 0
• Prior unresolved Codex findings still relevant: 0
• Active findings total: 0

The changes add terminalInteraction delivery, surface non-retryable turn errors with appropriate closure, and introduce targeted event subscriptions. Implementations align with protocol types and updated tests without introducing regressions.

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