feat(desktop): add collection-level type choice

[santosli]

Summary

• move User/Remote classification for collection imports into one header-level radiogroup
• apply the chosen type to every actionable child in the complete collection and select those children, while preserving imported/system/conflict/read-only state
• block collection eligibility, global selection counts, child selection, and final apply requests while actionable child types are unresolved or mixed
• keep standalone skill type controls and per-child import requests unchanged
• document and test full-collection, accessibility, selection, managed-type, and submit-path boundaries

Verification

• node --test apps/desktop/src/App.import-candidates.test.js apps/desktop/src/cardLayout.test.js (162 passed)
• npm test (280 passed)
• npm --workspace apps/desktop run build
• npm audit --audit-level=high (0 vulnerabilities)
• git diff --check
• visual QA at 1600x900 and 1000x760 with 0px document horizontal overflow

Visual evidence

• /tmp/skillbox-collection-type-required-blocked-1600.png
• /tmp/skillbox-collection-type-resolved-user-1600.png
• /tmp/skillbox-collection-type-user-1600.png
• /tmp/skillbox-collection-type-remote-1600.png
• /tmp/skillbox-collection-type-narrow-1000.png

No Rust, Tauri, filesystem, Git, or import-apply contract changes.