platform/app/webui: ship the power-watch scenario baked into the image

platform.LocalScenariosDir (/usr/share/bee/scenarios, populated from
iso/overlay/usr/share/bee/scenarios/ by build.sh's overlay rsync) is now
checked before removable media for both `bee run <name>` and the "6.
Scenario" page — a scenario shipped with the image works with no USB
stick required. ReadScenario/ListAvailableScenarios merge local + USB;
the removable-media-only functions from the previous commit are kept
as-is (still used directly where that's actually what's wanted) rather
than renamed out from under existing callers/tests.

iso/overlay/usr/share/bee/scenarios/nvbandwidth-all-gpu-power-watch.json
is a copy of scenarios/nvbandwidth-all-gpu-power-watch.json — the two
aren't auto-synced (documented in scenarios/README.md), so shipping a
scenario baked-in means checking it into both places.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

audit/internal/platform/export.go

@@ -247,3 +247,72 @@ func (s *System) ListScenarioFilesOnRemovableMedia() ([]ScenarioFileOnRemovableM
 	sort.Slice(out, func(i, j int) bool { return out[i].Name < out[j].Name })
 	return out, nil
 }
+
+// LocalScenariosDir is where scenario JSON files shipped with the ISO
+// itself live (rsync'd from this repo's scenarios/ into the overlay at
+// build time — see iso/builder/build.sh's "preparing staged overlay" step
+// and iso/overlay/usr/share/bee/scenarios/). Part of the read-only
+// squashfs, so a scenario here is always available with no USB stick
+// needed. A package var (not a const) so tests can point it at a temp dir.
+var LocalScenariosDir = "/usr/share/bee/scenarios"
+
+// ReadScenarioLocal reads scenarios/<name>.json from LocalScenariosDir.
+func (s *System) ReadScenarioLocal(name string) ([]byte, error) {
+	name = strings.TrimSpace(name)
+	if name == "" {
+		return nil, fmt.Errorf("scenario name is required")
+	}
+	return os.ReadFile(filepath.Join(LocalScenariosDir, name+".json"))
+}
+
+// ListLocalScenarioFiles lists the *.json files under LocalScenariosDir.
+func (s *System) ListLocalScenarioFiles() ([]ScenarioFileOnRemovableMedia, error) {
+	entries, err := os.ReadDir(LocalScenariosDir)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil
+		}
+		return nil, err
+	}
+	var out []ScenarioFileOnRemovableMedia
+	for _, e := range entries {
+		if e.IsDir() || !strings.HasSuffix(e.Name(), ".json") {
+			continue
+		}
+		out = append(out, ScenarioFileOnRemovableMedia{
+			Name:   strings.TrimSuffix(e.Name(), ".json"),
+			Device: "local (shipped with image)",
+		})
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].Name < out[j].Name })
+	return out, nil
+}
+
+// ReadScenario resolves scenarios/<name>.json, checking LocalScenariosDir
+// first (always available, no removable media required) and falling back
+// to ReadScenarioFromRemovableMedia. Prefer this over calling either one
+// directly unless you specifically need to restrict the lookup to one
+// source (as the tests for each do).
+func (s *System) ReadScenario(name string) ([]byte, error) {
+	if data, err := s.ReadScenarioLocal(name); err == nil {
+		return data, nil
+	}
+	return s.ReadScenarioFromRemovableMedia(name)
+}
+
+// ListAvailableScenarios merges ListLocalScenarioFiles (first) with
+// ListScenarioFilesOnRemovableMedia, for UIs that want to show everything
+// runnable via ReadScenario in one list.
+func (s *System) ListAvailableScenarios() ([]ScenarioFileOnRemovableMedia, error) {
+	local, err := s.ListLocalScenarioFiles()
+	if err != nil {
+		return nil, err
+	}
+	removable, err := s.ListScenarioFilesOnRemovableMedia()
+	if err != nil {
+		// A removable-media scan failure (e.g. no lsblk) shouldn't hide the
+		// scenarios that are always available regardless of media.
+		return local, nil
+	}
+	return append(local, removable...), nil
+}