fix(desktop): streamline managed runtime repair

[tulayha]

Summary

• Add a direct Repair VidXP action to broken Desktop-managed installation summaries.
• Open existing managed setup directly instead of routing through the first-install confirmation.
• Surface managed-runtime attention and repair controls before the feature list while preserving the saved feature selection.
• Keep Desktop-managed launchers private rather than publishing them to PATH, preserving lifecycle ownership, controlled launch configuration, version validation, and coexistence with externally installed CLI runtimes.
• No storage or model migration is required, and existing repositories do not need rebuilding.

Validation

• npm --prefix desktop run check — exercised TypeScript compilation, ESLint, 41 jsdom component tests, and the Vite production build. The component tests use mocked Tauri adapters and are not end-to-end Desktop validation.
• cargo test --locked --manifest-path desktop/src-tauri/Cargo.toml — exercised 81 Rust unit and lifecycle tests.
• npm --prefix desktop run model-catalog:check — verified the generated Desktop model catalog matches the canonical capability contracts.
• npm --prefix desktop run notices:check — verified generated third-party notices are current.
• git diff --check origin/main...HEAD — verified the PR diff has no whitespace errors.