test(theme-obsidian): add validation coverage for obsidian theme colors

[kanishka-2007-tech]

Description

Adds a dedicated test suite for the obsidian theme in lib/svg/themes.ts.

This test validates that the theme is correctly registered, contains valid hexadecimal color values, matches the expected design tokens, can be used by SVG generation utilities, and maintains sufficient contrast between background and text colors.

Changes

• Added lib/svg/themes/obsidian.test.ts
• Verified obsidian exists in the exported themes object
• Validated bg, text, and accent values are valid hex colors
• Checked expected color configuration:
• bg: 1a1a2e
• text: e2e8f0
• accent: f59e0b
• Added SVG color presence assertions (if SVG generator exists in repo)
• Added accessibility-oriented contrast validation
• Ensured all required theme properties are presen

Fixes #2319

Pillar

• 🎨 Pillar 1 — New Theme Design
• 📐 Pillar 2 — Geometric SVG Improvement

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.

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