feat: auto-pull, rebuild, and restart Symphony from GitHub

[silas-dsc]

Summary

• Symphony now polls its own git remote on a configurable interval; when new commits land on the tracked branch it fast-forward pulls, runs install (only when manifests changed) and the build command, then exits with code 75.
• New bin/symphony-supervisor.sh wrapper (also npm run start:watch) relaunches Symphony on exit 75 so hands-off upgrades work without an external process manager. Existing node dist/index.js users still get the pull + rebuild but exit instead of restarting.
• New auto_update: block in WORKFLOW.md controls enabled, interval_ms, remote, branch, repo_root, build_command, install_command. Defaults: every 5 min on origin/<current branch> of the Symphony checkout.

Safety

• Refuses to pull when the working tree is dirty, the local branch is ahead of the remote, or HEAD is detached without an explicit auto_update.branch.
• Install/build failures keep the previous build running — no restart is signalled.

Test plan

• npm run build clean.
• Drove SelfUpdater against a local bare repo: detected new commit, pulled, ran build, fired restart callback.
• Supervisor restart loop tested independently (3 runs, exit 75 twice, exit 0 once).
• Dirty-tree guard confirmed: skips with a clear warning.

https://claude.ai/code/session_01Bs7f7nqtcieCeknu9vuWys

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