UX-02: the panel was weaker than the startup gate for one field

Applying review finding N1, which was non-blocking because it fails closed, and
N2, which is a fabricated number.

N1. Clearing the `max_w` box answered HTTP 500 on a non-JSON body, which the
page rendered as "cannot reach the add-on" - untrue, and for the most prominent
limit field's most likely transient state. The cause was a disagreement between
two files that `inverter.py`'s own docstring says to keep in step:

  validate.py `_number()`  reads "" as "use the default", so rule 9 saw 2000
                           and was content
  inverter.py line 515     did a bare `float(opts.get("max_w", 2000))`, which
                           raises ValueError on ""

So a shape rule 9 TOLERATED could not be composed at all - the docstring's rule
inverted. The roster path never had this: `_entry_max_w` already guards. Only
the flat single-inverter path did. `_flat_max_w()` now reads empty as the
default exactly as `_number()` does, and unparseable as 0.0 exactly as
`_entry_max_w` does, where rule 9 refuses it by name at line 790.

⚠️ THE FIRST ATTEMPT AT THIS MADE IT WORSE, AND THE PROBE CAUGHT IT. Guarding
`build_roster` in `selfconfig` with `except: return validate(opts), []` turned
the 500 into ZERO PROBLEMS for `max_w: ""` - the validator has nothing to say
about it, so an empty list came back and the page would have ENABLED SAVE. A
crash became a silent acceptance. The guard is kept as a backstop for shapes
neither file anticipates, but it can no longer return an empty list: if the
roster cannot be composed and the validator names no reason, that disagreement
is itself reported.

MEASURED after the fix, `problems_and_ranges` with no HA:
  max_w 5000, slew_w 400   0 problems      (the live shape)
  max_w "",   slew_w 400   1 problem       rule 10, "against a site rail of
                                           2000 W" - clearing the box FAILS
                                           CLOSED on the live install rather
                                           than silently halving the rail
  max_w "",   slew_w 0     0 problems      accepted at the 2000 default
  max_w "abc"              1 problem       "max_w 'abc' is not a number"
Before the fix, both "" and "abc" raised ValueError instead.

N2. `translations/en.yaml:7` said "all 71 keys ... so ALL SEVENTY are rendered".
The 70->71 correction had been made in one half of the sentence and not the
other. 59-of-71 required is correct and was re-measured.

Suite: 24 files, all pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BwRLw7eKYj2byVdwB6kbjU

goodwe_controller/app/inverter.py

@@ -512,7 +512,7 @@ def build_roster(opts: dict, store, sign_cfg=None,
             soc_entity=opts.get("soc_entity", ""),
             batt_entity=opts.get("batt_entity", ""),
             batt_invert=bool(opts.get("batt_invert")),
-            max_w=float(opts.get("max_w", 2000)),
+            max_w=_flat_max_w(opts),
             # SAFETY-32. THE FLAT KEY, because this IS the single-inverter shape
             # - the one pack the flat options describe is the one pack whose
             # cut-out `bms_soc_floor` states. Defaulted from CFG-03's single
@@ -588,6 +588,36 @@ def _entry_bms_floor(entry: dict):
         return None
 
 
+def _flat_max_w(opts: dict) -> float:
+    """The single-inverter shape's cap, tolerating what rule 9 tolerates.
+
+    ⚠️ THIS USED TO BE A BARE `float(opts.get("max_w", 2000))` AND IT
+    DISAGREED WITH THE VALIDATOR. `validate.py`'s `_number()` reads `""` as
+    "use the default", so rule 9 looks at an empty `max_w` box, sees 2000 and
+    is content - while the bare `float("")` here raised ValueError from inside
+    `Controller.__init__`. Through UX-02's panel that surfaced as HTTP 500 on a
+    non-JSON body, which the page reported as "cannot reach the add-on": untrue,
+    and for the most prominent limit field's most likely transient state.
+
+    That inverted this module's own docstring rule - "keep the two in step: a
+    shape this tolerates that rule 9 does not name is a shape that runs" - in
+    the other direction: a shape rule 9 TOLERATED could not be composed at all.
+    The roster path never had the bug, because `_entry_max_w` below already
+    guards; only the flat path did.
+
+    Empty or absent is the default, exactly as `_number()` reads it.
+    Unparseable is 0.0, exactly as `_entry_max_w` reads it - and rule 9 refuses
+    it by name at line 790, with a sentence, before a control loop exists.
+    """
+    raw = opts.get("max_w", 2000)
+    if raw is None or raw == "":
+        return 2000.0
+    try:
+        return float(raw)
+    except (TypeError, ValueError):
+        return 0.0
+
+
 def _entry_max_w(entry: dict) -> float:
     """One entry's supervised cap, or 0.0 when it did not state a usable one.