fix: improve Tutor question quality and repetition

[ttbombadil]

Summary

• preserve the post-distinctness Tutor question when follow-up planning returns transition or blocked metadata
• add application-owned guidance requiring concrete identifiers and local code context for ambiguous sketch references
• keep real TutorPlan question overrides unchanged

Validation

• focused Tutor regressions: 2 passed
• Tutor/Course Content tests: 156 passed
• unit: 2,417 passed, 1 skipped
• integration: 13 passed, 1 skipped
• build, TypeScript, docs, diff, coverage passed
• Sonar Quality Gate passed; new coverage 81.8%, new violations 0, bugs 0, vulnerabilities 0, hotspots reviewed 100%

No Capacity, Tutor Registry SSOT, or client code changed. Do not merge automatically.

[ttbombadil]

Tutor Quality Stage 1 is now available for review in #113 and supersedes the implementation scope of this PR. The runtime fix and regression coverage from #112 are retained as ancestors and expanded by Stage 1. This PR remains open intentionally; no automatic close or merge was performed.