docs: apply cross-model doc-review fixes for v1.73.0.0

- README.md: host table gains the OpenClaw explainer arm row (setup has the
  arm; the table claimed to match setup)
- docs/skills.md: /review completeness-gaps section documents the
  gstack-shortcut(dec-<id>) acknowledged-debt suppression and orphan-marker
  flagging; /autoplan deep-dive states the recommended-option default with
  the 6 principles as tie-breakers
- CONTRIBUTING.md: host count 8 -> 10 (Hermes, GBrain), supported-hosts list
  completed
- docs/TESTING_INTERNALS.md: sandbox recipe says to source ~/.bashrc after
  the doctor seeds it; GSTACK_FREE_JOBS wording fixed from "caps" to
  "overrides in either direction" (matches the un-clamped runner)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/TESTING_INTERNALS.md

@@ -49,14 +49,16 @@ run green: run `scripts/sandbox-doctor.sh` once per boot. It documents and
 treats the full failure taxonomy (missing /dev/fd, 64M /dev/shm, spurious
 access(2) EACCES from the seccomp supervisor under load, full-capability
 processes defeating chmod-denial tests, no X server, no git identity, and
-Conductor's git-shim exit-code laundering). Then:
+Conductor's git-shim exit-code laundering). The doctor seeds `TMPDIR`,
+`DISPLAY`, and the runner knobs into `~/.bashrc`, so open a new shell (or
+`source ~/.bashrc`) before running the suite. Then:
 
 ```bash
 setpriv --ambient-caps=-all --bounding-set=-all bun run test
 ```
 
 Two runner knobs exist for these environments (both no-ops unless set):
-`GSTACK_FREE_JOBS` caps shard concurrency (2 is the measured sweet spot — one
+`GSTACK_FREE_JOBS` overrides the shard count in either direction (2 is the measured sweet spot — one
 serial mega-shard and 6-way sharding both saturate the per-process syscall
 supervisor), and `GSTACK_FREE_RETRY_FLAKY=1` re-runs attributed failures once
 serially, downgrading a clean retry to a loud FLAKY-PASS (capped at 5 files so