docs: fact-check the refreshed documentation against its sources

Numbers, API names, feature defaults and PR references checked against
CONFORMANCE.md, BENCHMARKS.md, CHANGELOG.md, the code and git history.

- int8 index figures (1.74x memory, 1.63x QPS) carry the dates git gives
  them (2026-09-19/20, machine not recorded, not re-run) instead of none;
  the Pi 5 1.18x carries 2026-09-21.
- BENCHMARKS headline: the libhdf5 chunked-write figure is the newest
  measurement (35x, 2026-09-23), not 45.3x (2026-08-03).
- Conformance counts follow the 2026-09-28 run (1 our-error, 2 ref-bug)
  in conformance/README.md, ROADMAP.md and CLAUDE.md, with a pointer to
  the bad_nbit_parms_walk.h5 flip.
- README: LZ4 is opt-in; the browser refuses reference/opaque/bitfield/
  time datasets too; zlib-rs byte-identity scoped to what was measured;
  macOS default links the system libz for inflate.
- Crate READMEs: system-zlib-decompress does something (macOS), SweepDetector
  lives in prefetch, checkpoint after more than 500 WAL entries, NetCDF-4
  unlimited-dimension size warning.
- agent-memory.md: string-dataset compression threshold, agents-md prints
  Markdown, float16 file sizes linked to their study.
- known-issues.md: contiguous selection reads, 1.21x vs h5py threads.
- docs/README.md, USE_CASES.md, ROADMAP.md, CLAUDE.md: range-read
  milestones M0-M5 and PRs #17-#19, missing README rows, CLI keygen/verify,
  dated figures, fast-math is not BLAS.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

crates/clawhdf5-accel/README.md

@@ -42,7 +42,8 @@ AVX2 and on NEON — with the `SDOT` instruction (through inline assembly,
 since the intrinsic is unstable) on cores that have dotprod, such as the
 Raspberry Pi 5, and plain NEON on older ones. At equal recall the int8
 index answers 1.63x the queries per second of the f32 one on x86-64
-(AVX2) and 1.18x on a Raspberry Pi 5 ([`BENCHMARKS.md`](../../BENCHMARKS.md)).
+(AVX2; 2026-09-20, machine not recorded, not re-run) and 1.18x on a
+Raspberry Pi 5 (2026-09-21) ([`BENCHMARKS.md` § Quantising the index copy](../../BENCHMARKS.md#quantising-the-index-copy-quantized_index)).
 
 The aarch64 code is compiled out on x86, so only the `test-arm64` CI job
 builds and tests it.