[core] Fix long report/funnel names overlapping header action buttons

[mrmeghana]

Problem

On report detail pages (e.g. a funnel), a very long title/name displayed in the shared cly-header overlaps the action buttons on the right (Edit / more-options). Because cly-header is reused across reports, the issue appears in all of them.

Root cause

The header's mid-level row is a flex row: a shrinkable left slot (bu-is-flex-shrink-1 + inline min-width:0) next to the right-side buttons. The left slot had no overflow handling, so overflowing content bled over the right slot instead of being clipped, and nothing pinned the buttons.

Fix

In _header.scss, for .cly-vue-header__level:

• clip the left slot's overflow so long content stays in its column;
• pin the right slot (flex-shrink: 0) with a 16px gap so the action buttons keep their natural width and position;
• ellipsize the default <h2> title.

This stops the overlap in every report using cly-header. Plugins with a custom header-left (e.g. funnels) additionally get proper ellipsis via their own small change.

Testing

Verified the compiled rules land in manifest.css and confirmed the flex/truncation behavior in an isolated reproduction of the header DOM (long name → ellipsis, buttons stay put; short name unchanged).

[mrmeghana]

Closing: per review on Countly/countly-platform#1072, the fix is being scoped to a funnel-specific class instead of the shared cly-header component. Since funnels is an enterprise plugin (not in this repo), there's no shared change to land here. The funnel fix lives in Countly/countly-enterprise-plugins#3367.