[codex] Add social post sharing

[mberman84]

What changed

• add one platform-neutral Copy social post action to the Loop Library homepage and every generated loop page
• copy ready-to-post text plus the canonical page URL instead of opening X
• provide visible success feedback and a selectable manual fallback when clipboard access fails
• regenerate all 31 loop detail pages and extend repository checks

Why

Visitors should be able to share Loop Library content on any social platform without being sent to a platform-specific composer.

Validation

• full Loop Library generation and validation suite
• 12 Worker tests
• SEO/GEO audit: 0 critical, high, or medium findings
• 32 social page screenshots validated
• here.now branding validator: 66 credits across 33 pages
• Codex autoreview: clean, no accepted/actionable findings