docs: comprehensive documentation overhaul

[RtlZeroMemory]

Summary

• Comprehensive docs overhaul across backend, protocol, styling, widgets, and dev docs.
• Corrected constants, defaults, type snippets, function signatures, and validation notes to match source.
• Updated MkDocs navigation, overrides, styles, and added missing widget documentation pages.

Scope

• Documentation-only changes (README.md, docs/**, mkdocs.yml, docs overrides/stylesheets).
• No runtime/package source code changes under packages/**.

Review Focus

• Information accuracy against current source contracts.
• Navigation and cross-link structure.
• Overall docs structure and readability.

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Fix Input example to use supported callback signature

The Grid docs include ui.input("name-input", { value: state.name, onChange: ... }), but ui.input only accepts (id, value, props?) or a single InputProps object, and InputProps uses onInput (not onChange) (packages/core/src/widgets/ui.ts and packages/core/src/widgets/types.ts). As written, this example fails type-checking and, if copied into untyped code, passes a non-string value that triggers runtime prop validation errors, so readers following this snippet will hit a broken integration path immediately.

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