Fix tag item association

[Herafia]

Checklist before requesting a review

Please delete options that are not relevant.

• I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
• I have updated the CHANGELOG with a short functional description of the fix or new feature.
• This change requires a documentation update.

Description

• It fixes !45879
• Assigning an item to a tag from the tag's details page no longer worked, without generating an error.

Regression : The file front/tag.form.php, which handled this association, had been accidentally deleted in an unrelated commit. The request was then processed by the generic mechanism, which created a tag instead of establishing the association.

Fix : re-enable correct processing of the tag/item association.

Screenshots (if appropriate):

[Rom1-B]

see comment

[Rom1-B]

Please rebase

[stonebuzz]

Fix should be added to GLPI 11 version too

[Rom1-B]

Missing entity-scope check: nothing here verifies the item's entity is within the tag's scope (entities_id + is_recursive), so a tag can be associated to an out-of-scope item. The 12.0-bf branch already carries this check; can you port it here?

Suggested change

	$item = new $itemtype();
	if (!$item->getFromDB($item_id) || !$item->canUpdateItem()) {
	throw new AccessDeniedHttpException(__s('You do not have permission to update this item', 'tag'));
	}
	if (
	isset($item->fields['entities_id'])
	&& $tag->fields['entities_id'] != $item->fields['entities_id']
	&& (
	!$tag->fields['is_recursive']
	|| !in_array($tag->fields['entities_id'], getAncestorsOf('glpi_entities', (string) $item->fields['entities_id']))
	)
	) {
	throw new AccessDeniedHttpException(__s('This tag is not available in the item entity', 'tag'));
	}

[stonebuzz]

testTagOutOfEntityScopeIsNotLinked() (present on 11.0/bugfixes, guards PluginTagTagItem::keepVisibleTags()) is deleted and its body replaced by the new test, with no explanation in the description. It covers a different code path (ticket form tag processing) and should be kept alongside the new test, not overwritten.