docs: add a source-verified GraphAgent architecture overview

[LeXwDeX]

Why

The Docs entry has no single overview of the current GraphAgent runtime. Readers need a map of the client transports, service composition, DAG execution, model calls, tools, and storage.

What changed

• Add docs/architecture.md with a Mermaid overview, component responsibilities, and source links.
• Add docs/architecture.html with the project's black-and-white architecture diagram.
• Link the overview from both README files.

Evidence

Verify the overview against main at 10806c9ad7. Show AppLayer as service composition, distinguish HTTP requests from SSE events, and explain the default AI SDK path and opt-in native model path. Describe SQLite state separately from workspace files, Memory YAML, and managed artifacts.

• Toolchain check: Bun 1.4.2, Node 24.21.0, Go 1.27.1.
• Prettier check passes for the two new documents; existing README formatting was preserved.
• All 64 checked local document/source links and line anchors resolve.
• Diagram single-file and accessibility checks pass.
• Chromium render checks pass for desktop, 390px mobile scrolling, and print layout.
• Staged whitespace check and final Astra review pass.

Checklist

• The document and diagram are under docs.
• Both README files provide an entry point.
• Source references and relative links resolve.
• The diagram has accessible labels and supports desktop, mobile scrolling, and print layouts.
• The pushed commit contains only these four documentation files.

Closes #701

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-03T07:14:29.013138Z	057b52f	Draft marked ready
🔒 Security Review	✅ Completed 2026-10-03T07:11:03.539208Z	057b52f	Draft marked ready

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[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 057b52f7ee

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[chatgpt-codex-connector]

Remove Hono from the runtime API label

The diagram places Hono inside the opencode service process, but the reviewed baseline constructs this server with Effect's HttpRouter and HttpApiApp (packages/opencode/src/server/server.ts:3-12,55-67,99-113), and packages/opencode has no Hono dependency or import; the repository's Hono usages belong to the unrelated packages/function and packages/enterprise services. This makes the source-verified overview direct readers toward a nonexistent runtime layer, so the label should describe only the Effect HTTP stack.

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