feat(navbar-vertical): add tooltipOverride to items

[spike-rabbit]

Allow consumers to override the automatic tooltip text (defaults to item label) on collapsed navbar items via a new tooltipOverride property on the item model. When provided, the tooltip is also enabled in the expanded state so it can be shown whenever needed.

Changes

• Added tooltipOverride?: TranslatableString to NavbarVerticalItemBase
• Updated [siTooltip] bindings to use item.tooltipOverride ?? item.label
• Updated [isDisabled] so tooltip stays enabled in expanded state when tooltipOverride is provided

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Documentation.
Examples.
Dashboards Demo.
Playwright report.

Coverage Reports:

• charts-ng
• dashboards-ng
• element-ng
• element-translate-ng
• maps-ng
• native-charts-ng

[gemini-code-assist]

Code Review

This pull request introduces a tooltipOverride property to vertical navbar items, allowing custom tooltip text to be displayed instead of the default item label. The review feedback highlights a potential issue where an empty string for tooltipOverride would still render an empty tooltip when collapsed, violating repository guidelines; it suggests explicitly disabling the tooltip in this scenario. Additionally, the feedback recommends updating the JSDoc documentation to accurately describe that the tooltip override is active in both expanded and collapsed states.

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