feat: add downloadable profile share card for social sharing

[Kokila-chandrakar]

Description

This PR introduces a shareable profile card feature that allows users to generate a visual representation of their DevTrack profile.

Changes Made

• Added a reusable ProfileShareCard component.
• Added a Generate Share Card button in the profile sharing section.
• Added profile card preview functionality.
• Added PNG download support using html-to-image.
• Included username, current streak, profile URL, and DevTrack branding in the generated card.

Benefits

• Makes sharing achievements more engaging.
• Improves social media visibility.
• Provides a visually appealing alternative to plain text sharing.

Fixes #1785

[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

[Kokila-chandrakar]

Hi @Priyanshu-byte-coder,

I checked the failing Playwright test (goal form posts a new goal). The failure appears to be related to the Goals widget, where the test is unable to find the "Add goal" button.

My changes in this PR are limited to the Share Profile / Share Card functionality, and I did not modify the Goals feature or its related components.

Could you please confirm whether this is an existing issue or if additional changes are required from my side?

Thank you.