Tighten doctor re-sync types: ReapplyOutcome enum and shared pack resolution #425

Problem

Two small type/duplication issues introduced or carried forward in #421:

1. ScopeReapplier.reapplyScope returns a Bool. true covers both "blocked because a configured pack cannot be produced" and "no packs to refresh". doctor --fix reads it as blocked, the tests call it blocked, and mcs update discards it via @discardableResult. The meaning lives only in the doc comment.
2. "Resolve identifiers or collect the unresolved" is written twice, in BootstrapCommand.runSync (declared packs) and ConfiguratorSupport.additivePackSet (configured extras). Both build a pack list plus an unresolved list, then report and throw.

Proposed fix

1. Return enum ReapplyOutcome { case applied, skipped } (or split skipped into blocked / nothingToDo if a caller needs it) so every call site reads clearly.
2. Add one helper on TechPackRegistry, e.g. packs(for ids:) -> (packs: [any TechPack], unresolved: [String]), and use it at both sites.

Found during review of #421.