Add optional insert-card button between cards

[ibci]

Summary

Adds a hover + affordance in the gap between cards (and above the first / below the last card) to insert a new card at that exact position, instead of only being able to append to the end of a list.

The feature is gated behind a new board setting "Show insert card button between cards" (off by default), so it does not change behavior for existing users unless they opt in.

Details

• Reuses the existing boardModifiers.insertItems flow (the same one powering the "Insert card before/after" context-menu items), so the new card opens in edit mode at the right index.
• The inserter element is marked data-ignore-drag — the same mechanism the card's menu button uses — so it does not interfere with drag-and-drop.
• Inserters are skipped in static/search views.

Files changed

• src/components/Item/Item.tsx — ItemInserter component + inline rendering between cards, gated on the setting
• src/components/Lane/Lane.tsx — passes laneIndex down to <Items>
• src/Settings.ts — the show-insert-card-button board toggle
• src/lang/locale/en.ts — setting label/description strings
• src/styles.less — inserter zone + button styles

Testing

• Lint (eslint) and prettier pass on the changed files; npm run build succeeds.
• Verified manually in Obsidian: toggling the setting on shows the + between cards and inserts at the correct position; drag-and-drop continues to work; toggling off restores stock behavior.

🤖 Generated with Claude Code