Polish Pattern Template UI: dialog sizing, KC editor layout, and conventions

- Fix dialog/canvas sizing: fit-content dialog follows canvas width, canvas
  max-width: 100% prevents overflow, horizontal resize supported
- Move pattern template dropdown above FPS/mode/smoothing in KC editor
- Remove emoji from pattern template dropdown options and auto-generated names
- Remove placeholder option from pattern template select, default to first
- Rename default pattern template from "Default" to "Full Screen"
- Add UI conventions to CLAUDE.md (hint pattern, select dropdown rules)

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

server/src/wled_controller/storage/pattern_template_store.py

@@ -41,7 +41,7 @@ class PatternTemplateStore:
 
         template = PatternTemplate(
             id=template_id,
-            name="Default",
+            name="Full Screen",
             rectangles=[
                 KeyColorRectangle(name="Full Frame", x=0.0, y=0.0, width=1.0, height=1.0),
             ],