docs: Migrate AGENTS.md to nested structure with agents.toml #11801

Job	Run time
Ready-to-merge gate / Missing "ready-to-merge" label	3s
diff_check	-1s
Build ${{ matrix.rn-architecture }} ${{ matrix.platform }} ${{ matrix.build-type }} ${{ matrix.ios-use-frameworks }}	-1s
Test ${{ matrix.platform }} ${{ matrix.build-type }} REV2	0s
	1s

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