#7159 - Top toolbar doesn't fit the frame in case of two ketcher instanses

[mariam-khutuashvili]

How the feature works? / How did you fix the issue?

(Screenshots, videos, or GIFs, if applicable)
The top toolbar collapsed its external-function buttons only below a fixed 650 px, a threshold last tuned in 2022. Buttons were added since, and the expanded toolbar now needs 732 px in the narrow layout, so every width between 650 and 732 px overflowed — which is exactly the width each instance gets on the duo page, pushing the zoom control outside the frame.

• getExpandedToolbarWidth computes the width the expanded toolbar actually needs from what is rendered: visible top-toolbar buttons at the icon size of the current container-query regime (28/32/40 px), the three dividers, the mode switcher (icon-only or labelled from 900 px), the zoom control and custom buttons. TopToolbar collapses when the panel is narrower than that.
• Hidden buttons are subtracted, so the toolbar no longer collapses early with hiddenControls — this also resolves Buttons are collapsed in the top toolbar because hidden buttons are not taken into account #3840.
• The old CUSTOM_BUTTON_ADDITIONAL_WIDTH = 40 is gone: custom buttons share the icon-button styles and are counted as such.

No rendering or test ids change. Verified in the browser: the duo page at 1498 px collapses both toolbars with no overflow; the single page swept from 1100 down to 560 px never overflows and collapses exactly where the buttons stop fitting; the #3840 URL at 690 px keeps its remaining buttons inline; the popup dialog (800 px) stays expanded as before, so no screenshot baselines move. Unit-tested against the measured widths of the three layout regimes.

Check list

• unit-tests written
• e2e-tests written
• documentation updated
• PR name follows the pattern #1234 – issue name
• branch name doesn't contain '#'
• PR is linked with the issue
• base branch (master or release/xx) is correct
• task status changed to "Code review"
• reviewers are notified about the pull request