Simplify toggleId to use filter instead of slice - #184

The toggleId function in RomList.vue was removing items from the selection array by reconstructing it with two slice calls, which allocates three arrays per deselection. This pattern also needed inline comments to explain what was happening, which is a sign the code wasn't self-describing.

Before:

function toggleId(selections: string[], id: string): string[] {
  const idx = selections.indexOf(id);
  if (idx !== -1) {
    // Remove selection
    return [...selections.slice(0, idx), ...selections.slice(idx + 1)];
  } else {
    // Add
    return [...selections, id];
  }
}

After:

function toggleId(selections: string[], id: string): string[] {
  return selections.includes(id)
    ? selections.filter((sid) => sid !== id)
    : [...selections, id];
}

Why it's better:

• Fewer allocations: filter does a single pass and creates one array instead of two intermediate slices plus a spread.
• More readable: includes + filter directly expresses intent — "if it's in there, remove it; otherwise add it" — without needing comments.
• Less code: 5 lines → 3 lines with no loss of clarity.

The behaviour is identical; this is a pure readability and minor performance improvement.

https://claude.ai/code/session_01XFx8U5RA5zMsnNwKB9inMZ