refactor: extract shared util package

[thdxr]

Summary

• add @opencode-ai/util and move shared host/runtime infrastructure out of Core
• rewrite CLI, Core, Server, TUI, Simulation, SDK Next, and V1 consumers to import Util directly without compatibility re-exports
• remove CLI test dependencies on Core database, event, project, and session internals and enforce the import boundary
• keep service discovery filenames and ports stable across release and preview channels

Verification

• workspace typecheck: 33/33 tasks passed in the pre-push hook
• CLI tests: 66 passed
• moved infrastructure tests: 101 passed
• SDK Next embedded tests: 7 passed
• TUI lifecycle tests: 2 passed
• CLI multi-platform build passed
• bun dev --standalone smoke test passed
• plain bun dev smoke test passed after restarting the stale shared service
• git diff --check passed