test(fuzz): fix nightly soak's division-by-zero and ClickHouse 26.2 modulo failures - #134

🟢 Confidence 10/10 · safe to merge. Test-only change; the new model floor is pinned by three fixed cases per target and the skip matcher is narrow and ClickHouse-gated.
_{no findings · tests covered · risk low}

Makes the fuzz oracle decline any / or % whose divisor folds to zero as the SQL parses it, and replaces the UNION-only 26.2 modulo known issue with a plan-level, execution-gated one. Test-side only, no production code, safe to merge.

• foldConstant folds an expression as asParsed reads it, refusing a zero divisor
• evaluate declines a zero-divisor / or % before any row is read
• knownPlanIssue narrows the 26.2 bug to a negative power-of-two divisor and gains executed
• Three fixed division cases replace the single one in queries.fuzz.test.ts

_{ba57dba · Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}