docs(telemetry): stop the harness contract narrating its own revisions

Notes across the workload contract described earlier versions of themselves, or
cited commits that only exist inside this chain. A squash merge publishes none of
it, so each reference resolves nowhere.

Notes that described their own earlier text:

- expected_spans.json: 'this note previously concluded', 'this note previously
  said', 'Un-skipped 2026-08-26', 'the reason had simply gone stale for two
  weeks' and 'the claim this entry carried' are replaced by the standing reason
  each entry holds. The wildcard pairs now say the validator globs the child via
  _span_name_matches(), and state the literal-collapse failure as what a
  different validator WOULD do rather than as history.
- regression-thresholds.json: 'an earlier version of this note wrongly claimed',
  'the earlier version oversold it' and 'an earlier note called that' become the
  cautions themselves -- do not reason from 'every ladder step is at least 2x',
  do not oversell the backstop, do not read a false fire as a missing override.
- test_check_regression_bounds.py: the docstring gives the reason a literal is
  wrong here, not the story of two tests that once hard-coded one.

Baseline-refresh history rewritten as measurement:

- README.md, baselines/README.md, telemetry-runbook.md and regression-metrics.json
  no longer attribute threshold moves to 'the 2026-08-26 refresh'. The evidence
  is kept as measurement -- span.tx.apply.p50 has read 0.7917 ms and 0.00597 ms
  on the same workload, 132x apart; job.acceptLedger.running.p95 has measured a
  5.74x floor on one baseline and 16.28x on another -- which is what supports the
  claim that a single-run baseline cannot bound these keys.

Two chain-only commit ids removed, d059f21bf3 and 3860c93db2. Neither is
reachable from develop, so both cease to exist on merge; the second is chain
bookkeeping. The facts they were cited for (the validator globs wildcards; the
span ladder's floor is 0.01 ms) are stated directly instead.

Capture provenance is deliberately kept: baseline-timings.json 'captured_at',
the 2026-08-26 baseline heading, and the 2026-08-24 figures cited as data.

Documentation, JSON note strings and one docstring only, no behaviour change.

.github/scripts/telemetry/test_check_regression_bounds.py

@@ -93,8 +93,7 @@ class CheckerCase(unittest.TestCase):
 
         Read from the scratch copies of the real inputs rather than written as
         literals, because a literal here is a copy of one particular baseline:
-        two of these tests previously hard-coded values from the 2026-08-24
-        capture and both broke the moment the baseline was refreshed, which is
+        a hard-coded figure breaks the moment the baseline is refreshed, which is
         the very drift check_regression_bounds.py exists to catch. Deriving the
         figure keeps the assertion pinned to the rule instead of to a snapshot.
         """