Documentation and onboarding materials updated to v0.9

[jacobsimionato]

[zeroasterisk]

Progress update:

PR #776 (docs file reorg) partially addresses this:

• ✅ Docs file structure reorganized to match nav sections
• ✅ React renderer status updated (merged, v0.8 stable)
• ✅ Renderer development guide now includes web_core shared library section (v0.9 aware)
• ✅ Community/ecosystem pages updated with contribution guide
• ✅ Comparison page updated (MCP Apps, ChatKit, AG UI)
• ✅ Client-setup guide has React section with install instructions
• ✅ Redirects for all moved files

Still needed for full v0.9 docs update:

• Quickstart/onboarding updated for v0.9 message flow (createSurface, updateComponents)
• Code examples migrated from v0.8 to v0.9 format
• Component gallery updated for v0.9 component format
• Data binding docs updated for v0.9
• Agent development guide updated for v0.9

Note: #812 (jacobsimionato) is also landing v0.9 renderer guide updates which will help close this.