fix(desktop): align collection header controls

[santosli]

Summary

• replace the collection header flex layout with stable identity/action grid tracks
• align Import as and collection selection controls to fixed action columns and a shared top baseline
• stack the action columns cleanly at the existing narrow breakpoint without changing import behavior

Verification

• node --test apps/desktop/src/cardLayout.test.js apps/desktop/src/App.import-candidates.test.js (162 passed)
• npm test (280 passed)
• npm --workspace apps/desktop run build
• cargo test -p skillbox-core --offline mutation_lock_preserves_parent_and_symlink_resolution_before_creation -- --nocapture (1 passed in the parent process and both subprocess roles)
• cargo clippy --workspace --all-targets --all-features --locked -- -D warnings
• git diff --check

GitHub's current Rust 1.98 runner introduced clippy::needless_late_init for an existing mutation-lock test helper. Commit test(core): satisfy current clippy lint rewrites only that test initialization without changing Rust product behavior.

Visual QA

• desktop collapsed: /tmp/skillbox-collection-header-alignment-collapsed-1600.png
• desktop expanded: /tmp/skillbox-collection-header-alignment-expanded-1600.png
• narrow expanded: /tmp/skillbox-collection-header-alignment-expanded-1000.png
• 1600px geometry: actions 470px, type 248px, selection 210px, shared top baseline, 0px page overflow
• 1000x760 geometry: actions move below identity while retaining 248px/210px tracks, 0px page/card overflow

No Rust, Tauri, import-contract, release, tag, or Homebrew changes.