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.)

.gitea/workflows/traceability-check.yml

@@ -94,7 +94,7 @@ jobs:
           #
           # Keep in sync with MIN_COVERAGE_PERCENT in scripts/extract-traces.ts;
           # scripts/extract-traces.test.ts fails if the two drift apart.
-          MIN_THRESHOLD=82
+          MIN_THRESHOLD=88
           if [ "$COVERAGE" -lt "$MIN_THRESHOLD" ]; then
             echo "❌ ERROR: Coverage ($COVERAGE%) is below minimum threshold ($MIN_THRESHOLD%)"
             exit 1