typecheck:core (the only blocking CI typecheck gate) runs against a
curated 27-file allowlist that excludes all src/app/(dashboard) TSX, and
next.config.mjs sets typescript.ignoreBuildErrors: true so next build
never type-checks it either. Orphaned-identifier regressions there (the
exact class fixed in #6625/#6909) were invisible to CI.
Adds tsconfig.typecheck-dashboard.json (extends tsconfig.json, scoped to
src/app/(dashboard)/**/*.ts(x)) plus check:dashboard-typecheck, a gate
script that runs tsc against it and diffs per-file/per-TS-code error
counts against a frozen baseline (config/quality/dashboard-typecheck-baseline.json,
262 pre-existing errors), following the same stale-enforcement allowlist
pattern as check-known-symbols. Only NEW errors beyond the baselined
count fail the gate; wired as a new blocking step in ci.yml (lint job)
and quality.yml (fast-gates).
Regression test (tests/unit/build/check-dashboard-typecheck.test.ts, 8
tests) reproduces the #6625/#6909 orphaned-identifier bug class against
the pure parseTscOutput/diffAgainstBaseline helpers.
