fix(heatmap): prevent tooltip overflow on rightmost cells

[mallya-m]

What does this PR do?

Fixes tooltip overflow on the rightmost cells of the contribution heatmap. Tooltip now flips to align right when near the viewport edge instead of overflowing.

Related issue

Closes #1046

Changes made

• Added isNearRightEdge check: true when weekIndex >= weekCount - 3
• Near right edge: tooltip uses right-0 translate-x-0 alignment
• Center cells: unchanged left-1/2 -translate-x-1/2 alignment
• Existing top/bottom flip logic unchanged
• No new dependencies

How to test

1. Go to dashboard → Contribution Heatmap
2. Hover over cells in the last 2-3 columns (far right)
3. Tooltip appears to the left, fully visible within viewport
4. Hover middle cells — tooltip still centers normally

[vercel]

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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

Quality (optional):

• 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

[mallya-m]

@Priyanshu-byte-coder could you please add gssoc:approved, level:intermediate, and type:bug labels? Thank you!

[github-actions]

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