fix: error state, leg grouping, prompt→generating transition

- log_parser: detect model load failure (child + router patterns) → state=error;
  switch to generating at progress=1.00 and at prompt eval summary line
- frontend: add state-error (llama flashes red, CSS variable override);
  group each leg+hoof in <g> so walk animation moves hooves with legs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/app.js

@@ -20,7 +20,7 @@
   // ── State class management ────────────────────────────────────────────────
   const ALL_STATES = [
     'offline','starting','loading','warming_up','idle',
-    'sleeping','waiting','processing_prompt','generating','unloading'
+    'sleeping','waiting','processing_prompt','generating','unloading','error'
   ];
 
   function applyState(stateName) {