fix(dashboard): add custom error UI for non-existent users

[krishnamanocha21]

Description

Fixes #64

This PR implements a custom, CommitPulse-themed Error UI for scenarios where a searched GitHub username does not exist.

Key Changes:

• Replaced the generic error boundary with a sleek "Broken Monolith" (🪨🔨) design.
• Utilized useParams to dynamically display the missing username in the error message (e.g., User "username" not found on GitHub).
• Hid the "Try again" button specifically for 404 errors, as retrying a non-existent user will not resolve the issue, ensuring the user is directed to the "Go back home" CTA instead.

Pillar

• 🎨 Pillar 1 — New Theme Design
• 📐 Pillar 2 — Geometric SVG Improvement
• 🕐 Pillar 3 — Timezone Logic Optimization
• 🛠️ Other (Bug fix, refactoring, docs)

Visual Preview

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 (CI will fail otherwise).
• My commits follow the Conventional Commits format (e.g., feat(themes): ..., fix(calculate): ...).
• I have updated README.md if I added a new theme or URL parameter.
• I have started the repo.
• I have made sure that i have only one commit to merge in this PR.
• The SVG output matches the CommitPulse "premium quality" aesthetic standard (no raw elements, smooth animations, correct fonts).

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[krishnamanocha21]

Hi @JhaSourav07, I've implemented the custom Error UI for non-existent users as requested in issue #64. I used useParams to make the error message dynamic and verified that it correctly triggers the 404 state without breaking the dashboard. Looking forward to your feedback!

[JhaSourav07]

can you focus on error SVG we get when someone puts wrong username instead?
i will change the Issue description.