UX-15: setup-only mode, and the wizard fixes F1, F2, meter, step 1

A new install names no inverter. When that is the startup gate's only
refusal, the add-on now serves the setup wizard in setup-only mode instead
of exiting 78. It builds no controller, MQTT client or meter task, its
HomeAssistant is read-only (every service call refuses before sending),
Controller refuses a read-only HomeAssistant, and /action answers 409.
Any other refusal still exits 78. DECISIONS/UX-15-setup-only-mode.md.

Wizard fixes from the UX-13 P4 test:
- F1: /config/validate converts what it can, so a conversion error blocks
  its own step and the live checks still run; save 422 carries steps.
- F2: saves send the model the page opened (base); only keys this page
  changed are written onto the blob stored now.
- A meter entity missing from Home Assistant is red on the last step.
- Step 1 says the reading went down after a skip that followed a fall.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

goodwe_controller/tools/ux13_wizard_blobs.py

@@ -11,7 +11,7 @@ The wizard edits the page model one step at a time and saves it through
 uipage.to_options(), like the Installer view. `blobs()` walks each step's
 choices (meter source and sign, one to three inverters, solar rows, every
 contract and price source, region, peak limit, shadow mode) from a new
-install and from the TEST-23 sites, and keeps what the shipped validator
+install as shipped, one with a power request entity, and the TEST-23 sites, and keeps what the shipped validator
 accepts, because the wizard saves nothing it refuses. test_setup.py checks
 the set; `--supervisor` runs it through Supervisor 2026.08.0's `AppOptions`
 offline, as the P2 test did. It touches nothing: no network, no Supervisor.
@@ -177,13 +177,14 @@ def apply(model, plan):
 
 
 def starts():
-    """(name, stored options) the wizard opens on: a new install (config.yaml's
-    defaults and one power request entity, typed in the Configuration tab so
-    the add-on starts) and the TEST-23 sites."""
+    """(name, stored options) the wizard opens on: a new install as shipped
+    (config.yaml's defaults, served in setup-only mode since UX-15), one with a
+    power request entity typed in the Configuration tab, and the TEST-23
+    sites."""
     sys.path.insert(0, os.path.join(HERE, "tools"))
     import ux13_demo as D
     new = dict(D.defaults(D.CONFIG), setpoint_entity="number.inv1_power")
-    out = [("new", new)]
+    out = [("empty", D.defaults(D.CONFIG)), ("new", new)]
     for f in sorted(glob.glob(os.path.join(HERE, "scenarios", "ux13", "test23",
                                            "*.json")))[:3]:
         out.append((os.path.basename(f)[:-5], dict(D.defaults(D.CONFIG),