Blast radius: exclude projection<=0 grades from the public model record

The degraded grades (projection=0 → model_value=0) are already settled in the
append-only ledger and must NOT be deleted (Data Semantics law). But their
hit/miss is noise, not model skill — they never had a real projection. So
getModelAggregate now filters `.gt('model_value', 0)` on both the settled and
pending queries: the rows stay in ledger_entries, but leave the public hit_pct /
CLV / per-tier record. `.gt` also drops NULL model_value. Post-fix no such row
can be written (projection<=0 refuses), so this only sheds the historical set.

This is the functional form of the "marking" the work order asked for — the
degraded locks are effectively marked as non-counting without mutating history.

Test builder mocks gained `.gt`; a lock asserts the filter is applied to both
queries. Suite 269/3253 green, web build exit 0.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/unit/ledgerService.test.js

@@ -24,6 +24,7 @@ function fakeSb() {
       not() { return b; },
       lt() { return b; },
       gte() { return b; },
+      gt() { return b; },
       in(col, ids) {
         if (b._update) {
           calls.updates.push({ values: b._update, ids });