fix(modal-fields): render user fields assigned to the basic group (issue #2045)

[ther12k]

Summary

When a user assigns a custom (user-typed) field to the 'Basic Information' group via the Modal Fields settings, the field silently disappears. The cause was a hardcoded skip in renderTaskModalFieldGroups:

if (groupConfig.id === "basic") {
    continue;
}

The skip was originally added to avoid double-rendering the built-in basic fields (title, details), which have dedicated creation paths in TaskModal (createTitleInput, detailsMarkdownEditor). Unfortunately, the same skip also discarded any user field the user moved into the basic group.

This change:

1. Removes the hardcoded basic-group skip.
2. Relies on the existing renderTaskModalField dispatcher to silently drop core basic fields (they are not in fieldRenderers, and they are not user fields, so renderTaskModalField returns false and they get counted in ignoredFieldIds). Their UI surfaces remain unchanged because the dedicated creation paths still run elsewhere.
3. Lets user fields in the basic group render through renderUserField exactly like they do in every other group.
4. Adds a guard at the end of the group loop that removes an empty task-modal__field-group container when the group produced zero rendered fields. This keeps the DOM clean for the basic group when it contains only core fields, and is also defensive against any future group whose fields are all core-only.

Tests

Updates tests/unit/modals/taskModalFieldRenderer.test.ts to reflect the new (correct) behavior — the previous expectations encoded the bug. Both tests now correctly report title/details as ignored, and assert that empty group containers are removed.

Adds tests/unit/issues/issue-2045-user-fields-in-basic-group.test.ts with three cases:

• User field moved into the basic group renders through renderUserField
• Groups whose fields all render keep their container (no regression)
• Core-only basic group produces no leftover empty container

All new + updated tests pass. Full tests/unit/modals suite (37 suites, 187 tests) passes. tsc --noEmit --skipLibCheck clean. npm run lint clean.

Verification

npm install
node generate-release-notes-import.mjs
npx tsc -noEmit --skipLibCheck
npx jest tests/unit/modals --no-coverage
node scripts/run-lint.mjs

Note

This PR is separate from PR #2051 (issue #2046 NLP input autofocus). They were developed in parallel as independent fixes.