docs: the README has drifted from the target table, and nothing checks the translation #592

What is wrong

The two top-level READMEs are outside every documentation check except the
emoji rule, and they have drifted from the implementation in three ways.

1. The translation is seven rows behind. README.md lists 21 targets and
README.zh-CN.md lists 14. The seven it lacks are every bare-metal row
(riscv64/riscv32-none-elf, thumbv6m, thumbv7m, thumbv7em-none-eabihf,
thumbv8m.main-none-eabi, armv7a-none-eabi/eabihf), and footnote 2, which
explains that a freestanding target takes its C library and emulator from a
board-support package, is absent as well. A reader of the 简体中文 README sees a
tool with no freestanding support: bare metal and freestanding occur zero
times in it. Heading count, code-block count and <details> count are all
equal between the two files, which is why nothing reported this.

2. The status column predates the third tier. The README knows yes and
planned. modules/toolchain-model/src/triple.cppm stores verified,
preview and planned, and the difference is load-bearing: prepare.cppm
refuses a build for a planned target, while preview builds and links. Three
rows the README calls planned are preview in the table it claims to mirror,
and three rows are missing entirely (x86_64-windows-musl, aarch64-none-elf,
x86_64-none-elf).

3. Surfaces shipped since 2026.8 are absent. Counting occurrences across
both files: accel, cuda, vulkan, sycl, device, runner,
build.mcpp, sbom, island, openkal — all zero. So are --release,
--profile and --features. The Documentation section names 7 of 31 chapters
and no chapter from parts 3x, 4x or 5x.

Smaller items in the same class: the footnote links to docs/40-baremetal.md
under the label docs/13, left behind by the renumbering in #590; mcpp why
is documented without its fourth topic, runners; the xlings repository is
spelled two different ways in one file; the English build-system bullet gained
a --configure-only clause the 简体中文 one never received; and both files
claim "43+ C++23 modules" against 119 module interface units under src/.

Why nothing caught it

.github/tools/check_docs_structure.sh rule 9 (relative links resolve) and
rule 10 (a translation carries the same tables and code blocks) both iterate
docs/ and examples/ only. The root README pair is in the file set of the
emoji rule and of nothing else, so the seven missing rows could stay green
indefinitely. A label naming a chapter number is checked by nothing at all.