Guard server removal when DNS proxy state exists

[thieso2]

Parent

#96

What to build

Prevent configured server removal from silently orphaning local DNS proxy state. Removing a server alias should inspect DNS proxy state and refuse if any installed proxy references that alias. A force option should remove the server config only while leaving historical DNS metadata intact for status and cleanup.

Acceptance criteria

• Removing a server with no matching DNS proxy state behaves as it does today.
• Removing a server whose alias is referenced by DNS proxy state fails with a clear message identifying the suffix and cleanup command.
• A force option removes the server config while leaving DNS proxy state intact.
• Forced removal preserves historical server alias and URL metadata in DNS state.
• Status can later display DNS state that references a missing server config without crashing.
• Tests cover normal removal, guarded refusal, forced removal, and missing-server diagnostics.

Blocked by

• Install a fresh proxy-backed macOS resolver #98