Add deterministic legal-text anchor coverage (lib, tool, retro harness)

legalTextAnchors.ts extracts typed anchors - money (currency-tagged,
attached-suffix and range-aware), percentages, ratio multiples, full
dates, durations, US and Canadian statutory citations, neutral and US
reporter case citations - canonicalized to value keys so $2.25M equals
$2,250,000 and 3/15/2027 equals March 15, 2027. anchorCoverage() diffs
sources against drafts in both directions (omission candidates and
grounding candidates) and audits words-vs-numerals pairs. Exposed as
the bounded library_anchor_coverage tool; scripts/anchor-coverage-
retro.ts measures any source/draft file sets with zero model calls.

Retro vs the LAB pilot autopsies: pilot-b-03 flags 4 of 13 judged
misses outright (March 15 2027 maturities x2, $218.75M TLA balance,
5-Business-Day grace) plus the 3.68x/1.24x computed-figure cluster in
reverse; pilot-b-01 grounding catches the model-computed 47.1%
combined share and an out-of-corpus 16 C.F.R. § 801.10 cite, and the
omission side surfaces the never-cited statutory framework (15 U.S.C.
§ 18a(b)(1)(B), Clayton §7A, FTC Act §13(b)) and all four precedent
reporter cites. 24 unit tests.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018bhP89cYSdEEjHNPnxacns