chore(ci): raise the traceability ratchet from 82% to 88%

Actual coverage is 90% (`bun run traces:coverage`), so the gate had ~8 points
of slack — a requirement could stop being traced and CI would not notice.
Per the ratchet policy in the workflow, move it up to sit just under the real
figure.

MIN_COVERAGE_PERCENT in scripts/extract-traces.ts moves in lockstep: the
workflow comment says to keep the two in sync and extract-traces.test.ts
asserts it, so changing only the YAML turns the frontend suite red.

(The stale "fails below 50%" comment in scripts/test-all.sh, wrong since the
threshold moved to 82, was corrected in the preceding commit along with the
rest of that file.)

scripts/extract-traces.ts

@@ -56,7 +56,7 @@ interface TracesData {
  *
  * TRACES: | DR-093
  */
-export const MIN_COVERAGE_PERCENT = 82;
+export const MIN_COVERAGE_PERCENT = 88;
 
 // Repo root, derived from this script's location (scripts/ -> repo root).
 // Must NOT be hardcoded to a developer's machine, or CI checkouts see no files.