chore: Minor cleanup flagged by newer gcc (#2140)

## Summary

Minor cleanup flagged by newer gcc:
- Removed unused variables
- Removed unimplemented function declaration
- `static` -> `inline` to avoid per-TU duplication

---

### AI Usage

Did you use AI tools to help write this code? _**NO**_

src/components/themes/BaseTheme.cpp

@@ -269,7 +269,6 @@ void BaseTheme::drawList(const GfxRenderer& renderer, Rect rect, int itemCount,
   if (selectedIndex >= 0) {
     renderer.fillRect(rect.x, rect.y + selectedIndex % pageItems * rowHeight - 2, rect.width, rowHeight);
   }
-  constexpr int maxValueWidth = 200;
   constexpr int minValueGap = 10;
 
   // Draw all items
@@ -358,8 +357,6 @@ void BaseTheme::drawHeader(const GfxRenderer& renderer, Rect rect, const char* t
 }
 
 void BaseTheme::drawSubHeader(const GfxRenderer& renderer, Rect rect, const char* label, const char* rightLabel) const {
-  constexpr int underlineHeight = 2;  // Height of selection underline
-  constexpr int underlineGap = 4;     // Gap between text and underline
   constexpr int maxListValueWidth = 200;
 
   int currentX = rect.x + BaseMetrics::values.contentSidePadding;