Pin the Node toolchain, remove runtime npm repair, make CI and E2E truthful

Phase 0 of the improvement plan (ai_prompts/prompt4.md): make the baseline
reproducible and stop the test runner from masking real failures.

- Pin Node >= 22.12 (engines + .nvmrc + engine-strict); every entry point
  fails fast with clear guidance instead of dying late with ERR_REQUIRE_ESM
  inside the packaging dependency graph.
- electron-launcher.js is diagnostics-only: all runtime npm install/rebuild/
  repair paths are removed. npm ci on the pinned toolchain is the only
  supported install path (README + GETTING_STARTED updated).
- Refuse to silently launch unsandboxed on Linux: --no-sandbox now requires
  an explicit STEPFORGE_ALLOW_NO_SANDBOX/ELECTRON_DISABLE_SANDBOX opt-in and
  is otherwise a hard error with actionable fixes; user-namespace sandboxing
  is detected and preferred.
- Click-capture E2E no longer converts startup crashes into "SKIPPED": the
  only allowed skip is the upfront absence of a display server. A missing
  shared library or crash now fails with the startup log. Same guard added
  to the startup smoke check.
- GitHub CI: run on pull_request, pin Node from .nvmrc, drop the macOS matrix
  entry (not a support target), and audit production and full dependency
  trees as separate signals. Gitea CI: pull_request trigger + pinned Node.
- Refresh package-lock on Node 22/npm 10 and remediate the form-data and
  undici advisories (npm audit: 0 vulnerabilities, prod and full tree).
- Stop tracking generated machine-specific build reports
  (build/build_report.md, build/artifacts_manifest.json).

Verified: 203 unit tests pass; repo-structure, startup-smoke, unit-workflows,
sample-artifacts, and build-release checks pass locally with a real Electron
launch. The click self-test now truthfully reports the pre-existing Linux
arm/debounce capture failures (also red on Gitea CI main run 177) instead of
hiding behind SKIPPED; that defect is scheduled for the capture-fix PR.

Co-Authored-By: Claude Fable 5 <[email protected]>

tests/checks/test_click_capture_selftest.sh

@@ -13,14 +13,22 @@
 #   arm:      warmup click ignored, first armed click captured
 #   debounce: 4 of 4  (40ms burst collapses to 1, three 300ms clicks kept)
 #
-# If the environment can't run a desktop capture at all (no display/stream),
-# the scenarios never print, so the check skips rather than failing CI.
+# Skip policy (kept honest on purpose): the ONLY allowed skip is the upfront
+# absence of a display server, detected BEFORE launching. Once the app is
+# launched, failing to reach the scenarios is a real failure — a startup
+# crash (missing shared library, launcher bug) must never be reported as
+# "no capture environment".
 
 set -euo pipefail
 
 ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
 cd "$ROOT_DIR"
 
+if [[ "$(uname -s)" == "Linux" && -z "${DISPLAY:-}" && -z "${WAYLAND_DISPLAY:-}" ]]; then
+  echo "click capture selftest SKIPPED: no display server (set DISPLAY or run under xvfb-run)"
+  exit 0
+fi
+
 TMP_ROOT="$(mktemp -d)"
 trap 'rm -rf "$TMP_ROOT"' EXIT
 
@@ -30,11 +38,17 @@ STEPFORGE_DATA_DIR="$TMP_ROOT/data" STEPFORGE_CLICK_SELFTEST=1 \
   timeout 120s npm start >"$LOG_FILE" 2>&1
 set -e
 
-# The self-test always prints this first line once it begins; without it the
-# app never reached the scenarios (couldn't launch / no capture environment).
+# The self-test always prints this line once the app is up (the frame source
+# is printed as a diagnostic even when no capture backend is available).
+# Its absence means the app never started — that is a failure, not a skip.
 if ! grep -q 'CLICK-SELFTEST source:' "$LOG_FILE"; then
-  echo "click capture selftest SKIPPED (no capture environment on this host)"
-  exit 0
+  echo "click capture selftest FAILED: the app never reached the self-test scenarios" >&2
+  if grep -Eq 'error while loading shared libraries' "$LOG_FILE"; then
+    echo "cause: Electron is missing system shared libraries on this host" >&2
+  fi
+  echo "----- startup output (last 40 lines) -----" >&2
+  tail -n 40 "$LOG_FILE" >&2
+  exit 1
 fi
 
 fail() {