fix: prevent username text overflow in Dashboard header on mobile (#1762)

[Akshita-2307]

Closes #1762

Problem

Username text overflows its container in the Dashboard header on mobile viewport, causing layout breakage.

Changes

• Added text-overflow: ellipsis with overflow: hidden and white-space: nowrap to the username element
• Ensured proper container width constraints for mobile viewports

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[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

Difficulty (pick one):

• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

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• quality:clean — ×1.2 multiplier
• quality:exceptional — ×1.5 multiplier

Validation (required to score):

• gssoc:approved — counts for points
• gssoc:invalid / gssoc:spam / gssoc:ai-slop — does not score

Type labels (type:*) are auto-detected from files and title. Review and adjust if needed.
Points formula: (difficulty × quality_multiplier) + type_bonus

[Priyanshu-byte-coder]

This PR has merge conflicts with main. Please rebase to unblock it:

git fetch origin
git rebase origin/main
# resolve conflicts, then:
git push --force-with-lease