Add AGENTS.md to latest-dash branch

[chgiesse]

Motivation

• Bring the repository guidance and contributor workflow documentation from the most recent PR into the latest-dash branch so the branch has the same repository-level instructions and conventions.

Description

• Add a new top-level file AGENTS.md containing repository layout, build/lint/test commands, code style conventions for Python and JS/TS, guidance for working in the monorepo, and notes on adding new files.
• The added document highlights key Flash backend areas, tooling notes, and formatting/linting expectations to help contributors follow local package configs.

Testing

• Verified the new file AGENTS.md exists at the repository root and inspected its contents to confirm the intended guidance was added, and the verification checks succeeded.
• No functional or unit tests were modified or executed as this is a documentation-only change.

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Codex Task

[github-actions]

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