Make Dashboard tree row metadata and actions responsive and consistent

[BorisTyshkevich]

Problem

Dashboard tree rows use inconsistent columns for counts and actions.

At normal sidebar widths:

• Dashboard counts are pushed into the right-side action area.
• Variables and Panels use a separate · count presentation.
• The Add panel (+) action is attached to the Dashboard row even though it creates a panel.

At narrow widths, the right-aligned metadata consumes space needed by the Dashboard and group names, producing aggressive truncation and an inconsistent hierarchy.

Expected behaviour

Use one row structure across Dashboard, Variables and Panels:

• Keep · count immediately after the row name.
• Reserve the rightmost area for action icons only.
• Move the Add panel (+) action from the Dashboard row to the Panels row.

At the narrow-sidebar breakpoint:

• Hide · count metadata entirely.
• Preserve as much space as possible for the Dashboard, Variables and Panels names.
• Keep applicable action icons in the rightmost action area.

Example at normal width:

• On-time flights · 7 … dashboard actions
• Variables · 4
• Panels · 7 … +

Example at narrow width:

• On-time flights … dashboard actions
• Variables
• Panels … +

Acceptance criteria

• Dashboard, Variables and Panels counts use the same inline · count placement directly after the label.
• The rightmost column contains actions only.
• Add panel appears on the Panels row and no longer appears on the Dashboard row.
• Narrow sidebar mode hides all Dashboard-tree dot/count metadata.
• Labels receive the recovered space and truncate only when still necessary.
• Expand/collapse controls and row actions remain usable by mouse and keyboard.
• Wider sidebar behaviour is restored when the sidebar is expanded.
• Browser regression coverage verifies both normal and narrow layouts.