style/standardize GitHub spelling

[Earnwithalee7890]

What changed? Why?
Standardized "Github" to "GitHub" across the documentation to ensure correct casing and brand consistency.

Notes to reviewers

• Targeted text content and link labels (e.g., "Open in Github" -> "Open in GitHub").
• Verified that URL paths were not broken (e.g., github.com lowercased in URLs remains untouched where necessary, but text descriptions are updated).

How has it been tested?

• Manual grep search to identify and replace instances.
• Verified file diffs to ensure no code or invalid URL changes.

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/2	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 1 Sum 2