docs: §8 fourth-mode refinements — Pillar-11 in-workspace anchor + corrected Passthrough/i8/i4+i2 tier split #652

Job	Run time
tier4-avx512-check	36s
native-backend/stable	8m 5s
wasm-simd/parity-node	48s
Pass MSRV values to other jobs	2s
nostd/thumbv6m-none-eabi/stable	29s
hpc-stream-parallel/rayon	1m 28s
clippy/1.95.0	1m 7s
format/stable	21s
neon-simd/parity-qemu	1m 4s
cross_test/${{ matrix.target }}/${{ matrix.rust }}	-1s
docs/nightly	-1s
cargo-careful	-1s
nightly-simd-polyfill	-1s
miri	-1s
tests/beta	12m 41s
tests/stable	11m 27s
tests/1.95.0	13m 23s
blas-msrv	44s
conclusion	0s
	52m 10s

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