docs: reconcile durable platform map with shipped chat

[imharrisonking]

Summary

• Update the Durable Automation Platform map to reflect the shipped Cloudflare Durable Object + Neon chat architecture and removal of Electric SQL.
• Keep Cloudflare's chat runtime adoption scoped; the general-purpose automation runtime remains undecided.
• Reframe iss-030 around future non-chat automation and update its dependency to iss-029.
• Add the next wayfinding sequence: domain boundary → broader runtime → API/MCP trust boundary → tracer bullet.

Validation

• kdb check .issues

[github-actions]

Preview Environment

Property	Value
Stage	pr-82
Web URL	https://d3i2t8r7e1ohje.cloudfront.net
API URL	https://d38zynyje879dw.cloudfront.net

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