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]>

docs/known-issues.md

@@ -138,7 +138,8 @@ before anything is written. On top of them:
 
 **Status:** open (documented 2026-09-26; re-checked 2026-09-28 in
 `Dataset::read_selection`, `crates/clawhdf5/src/reader.rs`). A selection
-read (and so the Python `ds[...]`) materialises only the selection's
+read (and so the Python `ds[...]`) of contiguous data copies just the
+selected runs; of chunked data it materialises only the selection's
 bounding box when that box covers at most half the dataset
 (`partial_read`). It decodes the whole dataset and extracts the selection
 instead when:
@@ -577,7 +578,8 @@ buffers per chunk and a second copy of the output, 4 KiB page faults on the
 output buffer, and element-by-element hyperslab copies. Re-measured at
 `c5334b1` (`BENCHMARKS.md`, "Results after in-place chunk decoding"):
 16-thread chunked deflate reads 4944 MB/s against 3135 for 16 h5py
-processes (1.58x), contiguous reads 1.29x h5py on one thread. Tests:
+processes (1.58x), contiguous reads 6718 MB/s against h5py's 5545 on one
+thread (1.21x; 1.29x h5py processes). Tests:
 `single_thread_decode_pool.rs`, `busy_decode_pool.rs`.
 
 ## Scale-offset data read back wrong values