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

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### AI Usage

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

lib/GfxRenderer/GfxRenderer.cpp

@@ -12,8 +12,6 @@
 
 namespace {
 
-const char* resolveVisualText(const char* text, std::string& visualBuffer, int paragraphLevel);
-
 /**
  * Resolves the requested style to the best available style in the given SD card font.
  * Falls back gracefully when the font lacks the requested variant.