fix(api): improve speed parameter validation and bounds handling

[Shweta2117409]

Description

Fixes #163

Improved speed parameter validation by enforcing safe animation bounds and graceful fallback handling.

Changes made

• Added min/max bounds validation for speed

• Invalid or extreme values now fallback to default 8s

• Added tests covering:

  • invalid formats
  • below minimum bounds
  • above maximum bounds

• Updated README parameter documentation for valid speed range

Pillar

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

Visual Preview

N/A (validation + test improvements only)

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.
• 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.
• (Recommended) I joined the CommitPulse Discord server for faster collaboration, mentorship, and PR support.

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[github-actions]

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Thanks for opening your first pull request — this is a big deal and we appreciate the effort!

While you wait for a review, please double-check:

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[Shweta2117409]

Implemented safer speed parameter validation with:

• min/max bounds handling
• graceful fallback to default 8s
• additional unit tests
• README documentation updates

All lint, tests, and typechecks are passing.

[Shweta2117409]

Closing this duplicate PR and continuing work in #208.

[Shweta2117409]

All local checks, tests, linting, and production build are passing successfully. The remaining Vercel check appears to be deployment authorization-related for external contributors.