Add target editing through API and UI

[nathanwhitbot]

Summary

• Add backend support for editing existing targets via PATCH /api/targets/{id}
• Persist mutable target fields and SSH metadata while preserving status/runtime state
• Wire an edit modal into the Targets UI and refresh the list after updates
• Add focused store/API coverage for target updates and capacity adjustment

Verification

• Worker reported focused Go tests and UI build/test checks completed
• git diff --check clean

[nathanwhitbot]

Resolved the merge conflict by rebasing this branch onto the latest main.

The only conflict was in ui/src/api.ts: main (#16, project editing) added a put<T> helper at the same spot where this PR added a patch<T> helper. Both are needed, so I kept both functions side by side. The rest of the changes auto-merged cleanly.

Verification after rebase:

• go build ./... — clean
• go test ./internal/... — all packages pass
• npm run build (tsc typecheck + vite) — clean
• git diff --check — clean

Force-pushed the rebased branch (history rewrite).