Implement OpenCode turn completion control plane

[danshapiro]

Summary

• implement OpenCode turn-complete using the OpenCode control plane instead of terminal BEL or CLI flags
• require confirmed session ownership before emitting terminal.turn.complete
• fix adversarial-review edge cases for ambiguous ownership, snapshot-seeded busy turns, and duplicated terminal panes

Tests

• npm run test:vitest -- --config vitest.server.config.ts test/unit/server/coding-cli/opencode-ownership-reducer.test.ts test/unit/server/coding-cli/opencode-activity-tracker.test.ts --run
• npm run test:vitest -- test/unit/client/store/selectors/paneTerminalSelectors.test.ts test/unit/client/components/App.ws-bootstrap.test.tsx --run
• FRESHELL_TEST_SUMMARY="OpenCode turn completion edge-case fixes before PR" npm run check

Notes

• origin did not have a dev branch, so I published the local dev branch as the PR base before creating this PR.