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.

---

### AI Usage

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Did you use AI tools to help write this code? _**PARTIALLY**_

---------

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

src/activities/reader/TxtReaderActivity.cpp

@@ -192,6 +192,17 @@ bool TxtReaderActivity::loadPageAtOffset(size_t offset, std::vector<std::string>
   }
   buffer[chunkSize] = '\0';
 
+  // Prime the SD card font's advance table with this chunk's codepoints.
+  // Without this, every getTextAdvanceX() call in the wrap loop below triggers
+  // on-demand glyph loads through the 8-slot overflow ring buffer, which
+  // thrashes for any text with more than 8 unique chars (i.e. all English),
+  // floods the heap with short-lived bitmap allocations, and eventually
+  // corrupts FreeRTOS state. The advance table persists across calls per
+  // font, so the cost amortizes to ~ASCII-size after the first chunk.
+  if (renderer.isSdCardFont(cachedFontId)) {
+    renderer.ensureSdCardFontReady(cachedFontId, reinterpret_cast<const char*>(buffer), /*styleMask=*/0x01);
+  }
+
   // Parse lines from buffer
   size_t pos = 0;
 
@@ -231,7 +242,7 @@ bool TxtReaderActivity::loadPageAtOffset(size_t offset, std::vector<std::string>
         break;
       }
 
-      int lineWidth = renderer.getTextWidth(cachedFontId, line.c_str());
+      int lineWidth = renderer.getTextAdvanceX(cachedFontId, line.c_str(), EpdFontFamily::REGULAR);
 
       if (lineWidth <= viewportWidth) {
         outLines.push_back(line);
@@ -242,7 +253,8 @@ bool TxtReaderActivity::loadPageAtOffset(size_t offset, std::vector<std::string>
 
       // Find break point
       size_t breakPos = line.length();
-      while (breakPos > 0 && renderer.getTextWidth(cachedFontId, line.substr(0, breakPos).c_str()) > viewportWidth) {
+      while (breakPos > 0 && renderer.getTextAdvanceX(cachedFontId, line.substr(0, breakPos).c_str(),
+                                                      EpdFontFamily::REGULAR) > viewportWidth) {
         // Try to break at space
         size_t spacePos = line.rfind(' ', breakPos - 1);
         if (spacePos != std::string::npos && spacePos > 0) {
@@ -354,12 +366,12 @@ void TxtReaderActivity::renderPage() {
             // x already set to left margin
             break;
           case CrossPointSettings::CENTER_ALIGN: {
-            int textWidth = renderer.getTextWidth(cachedFontId, line.c_str());
+            int textWidth = renderer.getTextAdvanceX(cachedFontId, line.c_str(), EpdFontFamily::REGULAR);
             x = cachedOrientedMarginLeft + (contentWidth - textWidth) / 2;
             break;
           }
           case CrossPointSettings::RIGHT_ALIGN: {
-            int textWidth = renderer.getTextWidth(cachedFontId, line.c_str());
+            int textWidth = renderer.getTextAdvanceX(cachedFontId, line.c_str(), EpdFontFamily::REGULAR);
             x = cachedOrientedMarginLeft + contentWidth - textWidth;
             break;
           }