docs: Enhance Customization Guide with Troubleshooting and FAQ Section

[VanshikaSingh28]

Description

Fixes #6241

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).
• (Recommended) I joined the CommitPulse Discord community for contributor discussions, mentorship, and faster PR support.

[vercel]

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[retenta-bot]

This PR enhances the documentation by adding a Troubleshooting and FAQ section, which is crucial for user support and experience. It aligns with our previous decision to improve user experience through better documentation. If you have any questions or need further assistance, feel free to reach out. Happy coding!

[github-actions]

📦 Next.js Bundle Size Report (Gzipped Sizes)

✨ No significant bundle size changes detected.

📊 Summary of Totals

Category	PR Size	Base Size	Difference
Total JS	5005.04 KB	5005.04 KB	0 B
Total CSS	354.80 KB	354.80 KB	0 B

[Aamod007]

It looks like this PR adds the Table of Contents including the 'Troubleshooting & FAQ' link, but the actual 'Troubleshooting & FAQ' section content itself is missing from the diff! Could you please push the rest of the changes so the link actually points to something? Once the section is added, I'll be happy to approve.