Implement port allocation

[nickbeau]

Detail: Allocate and persist loopback ports for local Symphony instances.

Milestone: Sprint 7: Local Process Runner

Source: docs/technical.md sprint plan.

[nickbeau]

I reviewed issue #65 and am implementing local-process port allocation in the import shell creation path. I’ll add backend allocation to assign a free loopback port for LocalProcess instances, persist it with the instance, and update repository import defaults/UI + tests to cover automatic allocation and uniqueness.

[nickbeau]

I’ve reviewed issue #65 and the local implementation. I’m tightening the patch now, then I’ll run the repository test/build checks before rebasing onto main and opening the PR.

[nickbeau]

I’m continuing the issue #65 implementation in the current worktree. I’m reviewing the existing local diff now, then I’ll run the project validation, rebase onto main, push the branch, and open a PR if the checks are clean.