⚡ Remove duplicate manifest link and optimize PWA config

[google-labs-jules]

💡 What: Removed the redundant site.webmanifest link and file, and consolidated the configuration into manifest.json.
🎯 Why: To reduce HTTP requests (performance) and fix conflicting theme colors (correctness).
📊 Measured Improvement: Reduced initial request count by 1. Standardized PWA metadata.

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PR created automatically by Jules for task 2156754249081773161 started by @xRahul

[google-labs-jules]

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