docs: add GitHub Pages publication plan

[CoderDeltaLAN]

Summary:

• Add a GitHub Pages publication plan.
• Document publication options, activation checklist, source and post-activation verification.

Scope:

• one documentation file
• no Pages activation
• no HTML changes
• no secrets
• no generated artifacts

Validation:

• local verification passed
• staged diff reviewed
• pre-push checks passed
• branch push verified