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/webui/page_scenario.go

@@ -1,28 +1,31 @@
 package webui
 
-// renderScenario renders the "6. Scenario" page: scenarios/*.json files
-// found on any mounted removable media (e.g. the blackbox USB stick),
-// each runnable with one click. A run is enqueued as a normal Task
-// (target "scenario") — progress/logs live in Tasks like every other SAT
-// pack, no separate live-output UI needed here.
+// renderScenario renders the "6. Scenario" page: every scenarios/*.json
+// runnable via platform.System.ReadScenario — the ones shipped with the
+// image (platform.LocalScenariosDir) plus anything found on mounted
+// removable media (e.g. the blackbox USB stick) — each runnable with one
+// click. A run is enqueued as a normal Task (target "scenario") —
+// progress/logs live in Tasks like every other SAT pack, no separate
+// live-output UI needed here.
 //
 // See audit/internal/platform/scenario.go for the scenario file format and
-// scenarios/README.md for the drop-a-file-on-the-USB-stick workflow this
-// page is built around.
+// scenarios/README.md for how to add one (shipped in the image, or dropped
+// on the USB stick for a one-off/air-gapped run).
 func renderScenario(opts HandlerOptions) string {
 	return `<p style="color:var(--muted);font-size:13px;margin-bottom:16px">
   Scripted, ad-hoc test scenarios — commands plus background samplers (IPMI
   sensors, nvidia-smi, ...), described in a small JSON file instead of a
-  hardcoded test. Drop a <code>&lt;name&gt;.json</code> file under
-  <code>scenarios/</code> on a removable drive (e.g. the same USB stick
-  already plugged in for blackbox) and it shows up below — no rebuild
-  needed. Runs are enqueued like any other task; watch progress in
+  hardcoded test. The list below includes scenarios shipped with this image
+  as well as any <code>&lt;name&gt;.json</code> dropped under
+  <code>scenarios/</code> on a mounted removable drive (e.g. the same USB
+  stick already plugged in for blackbox) — no rebuild needed for the
+  latter. Runs are enqueued like any other task; watch progress in
   <a href="/tasks">Tasks</a>.
 </p>
 
 <div class="card">
   <div class="card-head">
-    <span>Scenarios found on removable media</span>
+    <span>Available scenarios</span>
     <button class="btn btn-sm btn-secondary" type="button" onclick="scenarioRefresh()">&#8635; Refresh</button>
   </div>
   <div class="card-body">
@@ -38,7 +41,7 @@ function scenarioRefresh() {
     .then(r => r.json())
     .then(files => {
       if (!files || !files.length) {
-        list.innerHTML = '<p style="color:var(--muted);font-size:13px">No scenarios/*.json found on any mounted removable media.</p>';
+        list.innerHTML = '<p style="color:var(--muted);font-size:13px">No scenarios found — none shipped with this image and none under scenarios/ on mounted removable media.</p>';
         return;
       }
       let html = '<table class="table"><thead><tr><th>Name</th><th>Found on</th><th></th></tr></thead><tbody>';