fix(ui): show keyboard focus on sidebar toggler

[mukul190303]

Description

Adds a visible focus indicator to the sidebar hamburger toggler when it receives keyboard focus.

The application globally removes button outlines, making the toggler’s focus state invisible while navigating with the Tab key. This change uses :focus-visible so keyboard users receive a clear indicator without changing mouse-click styling.

Addressed Issue

Fixes #1202

Testing

• Verified the change targets the .navbar-toggler elements rendered by SidebarToggler
• Confirmed the existing global button focus rule is overridden
• git diff --check passes

[owasp-dt-bot]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues

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