fix: Prepare SD card font caches from txt reader (#1973)

## Summary

SD card font fixes:
- `TxtReaderActivity` needs to call `renderer.ensureSdCardFontReady` to
build the advance lookup table to support rendering with SD card fonts.
This revealed that `TxtReaderActivity` was inconsistently performing
layout with `getTextWidth`, when the renderer actually uses
`getTextAdvanceX`, which can lead to minor inconsistencies in alignment.
- Avoid allocating one big `allText` string in
`ParsedText::layoutAndExtractLines`. Instead, pass the vector of word
strings directly to `SdCardFont::buildAdvanceTable`, where the algorithm
just needs to iterate codepoints anyway.

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Co-authored-by: Justin Mitchell <justin@jmitch.com>

lib/GfxRenderer/GfxRenderer.h

@@ -94,6 +94,8 @@ class GfxRenderer {
   // (which holds a const GfxRenderer&) before measuring word widths. Safe to call on non-SD fonts (no-op).
   // styleMask: bitmask of styles to prepare (bit 0=regular, 1=bold, 2=italic, 3=bold-italic).
   void ensureSdCardFontReady(int fontId, const char* utf8Text, uint8_t styleMask = 0x0F) const;
+  void ensureSdCardFontReady(int fontId, const std::vector<std::string>& words, bool includeHyphen,
+                             uint8_t styleMask = 0x0F) const;
 
   // Orientation control (affects logical width/height and coordinate transforms)
   void setOrientation(const Orientation o) { orientation = o; }