build(gate)!: coverage leaves the gate and runs on demand

Both lanes printed a coverage total with no threshold (owner decision E32
D4). No real hit as a lane: the one time the number found anything (5 bugs,
E32) it was read by hand, and since then it was a line nobody acted on. It
was also the most expensive part of the vitest lane, and the run that
flaked in E35 S1. The vitest lane runs without --coverage, the pytest lane
runs plain pytest; docs/development.md gives both on-demand commands, and
the register row says why.

frontend/src/lib/gates.snapshot.json

@@ -2110,10 +2110,7 @@
       "    volumes:",
       "      - ./:/app",
       "    working_dir: /app",
-      "    command:",
-      "      - sh",
-      "      - -c",
-      "      - 'python -m pytest --cov=app --cov-report= ; rc=$$?; echo \">> backend coverage (app/) $$(python -m coverage report --format=total)% of lines\"; exit $$rc'"
+      "    command: [\"python\", \"-m\", \"pytest\"]"
     ],
     "frontend/.prettierignore": [
       "dist",
@@ -2238,7 +2235,7 @@
       "    pip-audit -r requirements.lock --no-deps --disable-pip",
       "}",
       "if [ \"$mode\" = all ]; then",
-      "  lane \"vitest (+ coverage report)\" frontend npm run --silent test -- --coverage",
+      "  lane \"vitest\" frontend npm run --silent test",
       "  lane \"vite build\" frontend npx vite build --logLevel warn",
       "  lane \"pytest (pure-logic + DB lane)\" pytest_lane",
       "  lane \"pip-audit (backend lock)\" pip_audit",