fix: initialize standalone toolbar

[michalsn]

Description
This PR fixes a bug where the Debug Toolbar loaded from ?debugbar_time=... (via Debugbar-Link headers for AJAX/non-HTML responses) appeared but was not interactive.

The fix adds a dedicated standalone bootstrap script for this mode, while keeping toolbar.js focused on core toolbar behavior. It also provides a loadDoc() fallback only when the main loader flow is absent, so the History section keeps working on standalone toolbar pages.

Fixes #9949

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[datamweb]

ciDebugBar.init() assumes that #toolbarContainer exists for both JavaScript and CSS theme handling, but on standalone debugbar pages (?debugbar_time=...) this element is missing. Falling back to document.body avoids errors, however without assigning the expected ID the existing CSS no longer matches, so the theme toggle appears non-functional.

Suggested change

	this.toolbarContainer = document.getElementById("toolbarContainer") || document.body;
	this.toolbarContainer = document.getElementById("toolbarContainer");
	if (!this.toolbarContainer) {
	this.toolbarContainer = document.body;
	if (!document.body.id) {
	document.body.id = "toolbarContainer";
	}
	}

[michalsn]

You're right about the theme toggler - I'll fix that. But I'll keep standalone bootstrapping in a separate file to preserve clear responsibility boundaries.

[datamweb]

Appreciate you taking the time to explain your reasoning.

[datamweb]

LGTM!
In general, many of the existing issues in the debugging tools seem to stem from insufficient test coverage as well, which might be worth addressing over time.