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/EpdFont/SdCardFont.h

@@ -1,6 +1,8 @@
 #pragma once
 
 #include <cstdint>
+#include <string>
+#include <vector>
 
 #include "EpdFont.h"
 #include "EpdFontData.h"
@@ -43,10 +45,11 @@ class SdCardFont {
   int prewarm(const char* utf8Text, uint8_t styleMask = 0x0F, bool metadataOnly = false);
 
   // Build a compact advance-only table for layout measurement.
-  // Extracts ALL unique codepoints from utf8Text (no MAX_PAGE_GLYPHS cap),
+  // Extracts ALL unique codepoints from words (no MAX_PAGE_GLYPHS cap),
   // batch-reads advanceX from SD, stores in a sorted per-style table.
   // Returns number of codepoints not found in font coverage.
   int buildAdvanceTable(const char* utf8Text, uint8_t styleMask = 0x0F);
+  int buildAdvanceTable(const std::vector<std::string>& words, bool includeHyphen, uint8_t styleMask = 0x0F);
 
   // Look up advanceX for a codepoint from the advance table.
   // Returns the 12.4 fixed-point advance, or 0 if not found.
@@ -236,6 +239,9 @@ class SdCardFont {
   void applyKernLigaturePointers(PerStyle& s, EpdFontData& data) const;
   void applyGlyphMissCallback(uint8_t styleIdx);
   int32_t findGlobalGlyphIndex(const PerStyle& s, uint32_t codepoint) const;
+  int fetchAdvancesForCodepoints(uint32_t* codepoints, uint32_t cpCount, uint8_t styleMask);
+  template <typename Iter>
+  int buildAdvanceTableRange(Iter begin, Iter end, bool includeSpace, bool includeHyphen, uint8_t styleMask);
   int prewarmStyle(uint8_t styleIdx, const uint32_t* codepoints, uint32_t cpCount, bool metadataOnly);
 
   // Global helpers