T06: wire cost into the loop

- InnerLoop definition-of-done gains a cost row: M-D2-CST may no longer
  be recorded uncomputable, and composition must be reported, not only a
  total.
- InnerLoop Step 5 gains the --self-test contract: every tool that
  reports a number exposes one, and it runs before the number does.
  Rationale attached, because the case that motivated it is the one
  review cannot catch — survey and reviewer both verified the same large
  sample and both missed the small one.
- make cost / cost-test / cost-pin on the one command surface; cost-test
  in `make all` and in CI.
- Hub now holds the measured figure for CB-WP-0001: 80.6M in / 323.6k
  out against the 401,100 it previously estimated, low by ~200x. The
  event states plainly that the hub schema cannot represent the 88% of
  cost that is cache, and names `make cost-pin` as the authority.

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

research/CB-RES-0002-cost-accounting.md

@@ -101,7 +101,7 @@ the `subagents/` tree, so first-wins dedup under-counted it. See
 The subagent line is not a footnote. C1's blind-spot finding says a
 collector reading only the main file under-reports; a target of $92.21 would
 have been hit only by a collector *with* that blind spot, and failed by a
-correct one. The acceptance target is **$92.87, stated as its two
+correct one. The acceptance target is **$93.32, stated as its two
 components**, so a collector reading one tree is diagnosed rather than
 merely failed.