Docs overhaul: restructure nav and B20 specs

[mindapivessa]

Summary

• Restructure site navigation with new Get Started, Build on Base, and Chain tabs
• Move B20 spec under Specifications section in Chain tab, organized by feature
• Remove standalone Specifications tab
• Add B20 changelog and demo link
• Rename Protocol Specifications → Specifications, flatten Protocol subgroup

Test plan

• Verify nav structure renders correctly in preview
• Confirm B20 spec, changelog, and demo link are accessible
• Check no broken links from removed pages

🤖 Generated with Claude Code

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Project	Status	Preview	Updated (UTC)
base	🟢 Ready	View Preview	Aug 18, 2026, 6:06 PM

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[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	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 0 Sum 1