Implement local process runner

[nickbeau]

Detail: Add runner support for starting Symphony as a local process from a release artifact.

Milestone: Sprint 7: Local Process Runner

Source: docs/technical.md sprint plan.

[nickbeau]

I’m starting work on this. I’ve confirmed the issue scope and will inspect the Sprint 7 technical plan plus existing runner/release abstractions before making changes.

[nickbeau]

I’ve confirmed the scope for this issue: implement the local process runner for Symphony release artifacts, including release resolution, extraction/cache, environment injection, start/stop/restart behavior, and tests/docs. I’m reviewing the current worktree changes now so I can either complete them safely or tighten them up before validation.