test(ShareSheet-responsive-breakpoints): ShareSheet responsive breakpoints and mobile viewport layout

[Subhooo5]

Description

Fixes #2619

• Added responsive breakpoint and mobile viewport layout tests for ShareSheet. Asserts w-full + max-w-[380px] on the modal panel, p-4 on the backdrop overlay, grid grid-cols-2 wrapping all 4 social buttons, w-full on all 5 export buttons, and clean mounting when matchMedia reports a 375px mobile viewport. All assertions target Tailwind class names in markup — no CSS rendering assumed.

Pillar

• 🛠️ Other (Bug fix, refactoring, docs)

Checklist before requesting a review:

• I have read the CONTRIBUTING.md file.
• I have tested these changes locally (localhost:3000/api/streak?user=YOUR_USERNAME).
• I have run npm run format and npm run lint locally and resolved all errors.
• My commits follow the Conventional Commits format.
• I have starred the repo.
• I have made sure that i have only one commit to merge in this PR.

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[Subhooo5]

Hey @JhaSourav07 Test added successfully. All existing tests pass locally. Feel free to review, add necessary labels and merge it. 🫂🚀