Fix absolute Windows path in docs/site/manifest.json for cross-platform compatibility

[coderabbitai]

Issue Description

The source_base_path in docs/site/manifest.json is currently set to an absolute Windows path (C:/Users/user/Desktop/osmodoc), which will cause cross-platform build issues.

Problem

Using absolute paths breaks builds on different operating systems and development environments.

Suggested Solution

Change the absolute path to:

• A relative path (e.g., "../.." or repository root)
• Use a DocFX variable for better portability

Context

This issue was identified during code review to ensure cross-platform compatibility.

Backlinks

• PR: feat: update project logic for nuget integration #39
• Comment: feat: update project logic for nuget integration #39 (comment)
• Reported by: osm-Jatin

[osm-Jatin]

Issue is handled in this PR: #52