docs: fix cross-links after the refresh; remove the stale benchmark script

- docs/README.md links the improvement logs and June plans where the
  refresh archived them (docs/archive/).
- clawhdf5-py README: 'r+' creates and replaces attributes (compact or
  dense); only deleting them is unsupported.
- scripts/run-benchmarks.sh benchmarked the pre-rename rustyhdf5-format
  and overwrote BENCHMARKS.md; nothing referenced it. Removed.
- Cargo.toml descriptions no longer name rustyhdf5/edgehdf5; clawhdf5-gpu
  says it is not HDF5 I/O.
- benchmarks/cross_platform.sh pointed at a ROADMAP section that no longer
  exists.

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

CLAUDE.md

@@ -254,8 +254,9 @@ python -m pytest crates/clawhdf5-py/tests      # compares with h5py; editing tes
 - Run on an idle machine (1-minute load average below 2; wait otherwise),
   alternate base and candidate binaries for A/B comparisons, and record date,
   machine, commit and command with every number in `BENCHMARKS.md`.
-- `scripts/run-benchmarks.sh` is stale (it benchmarks `rustyhdf5-format` and
-  overwrites `BENCHMARKS.md`) — do not run it.
+- `BENCHMARKS.md` is written by hand from dated runs; no script regenerates
+  it (the old `scripts/run-benchmarks.sh`, which benchmarked the pre-rename
+  `rustyhdf5-format` and overwrote the file, was removed on 2026-09-28).
 
 ### CLI
 ```bash