docs: §8 fourth-mode refinements — Pillar-11 in-workspace anchor + corrected Passthrough/i8/i4+i2 tier split #653

Job	Run time
tier4-avx512-check	46s
clippy/1.95.0	33s
neon-simd/parity-qemu	53s
native-backend/stable	7m 3s
hpc-stream-parallel/rayon	1m 28s
wasm-simd/parity-node	1m 0s
nostd/thumbv6m-none-eabi/stable	35s
format/stable	21s
Pass MSRV values to other jobs	3s
nightly-simd-polyfill	0s
tests/stable	11m 36s
blas-msrv	57s
tests/1.95.0	11m 40s
tests/beta	11m 13s
miri	-5s
docs/nightly	-9s
cross_test/${{ matrix.target }}/${{ matrix.rust }}	-9s
cargo-careful	-10s
conclusion	-1s
	47m 34s

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