fix: prevent Serial.printf from blocking when USB disconnected

On ESP32-C3 with USB CDC, Serial.printf() blocks indefinitely when USB
is not connected. This caused device freezes when booted without USB.

Solution: Call Serial.setTxTimeoutMs(0) after Serial.begin() to make
all Serial output non-blocking.

Also added if (Serial) guards to high-traffic logging paths in
EpubReaderActivity as belt-and-suspenders protection.

Includes documentation of the debugging process and Serial call inventory.

Also applies clang-format to fix pre-existing formatting issues.

lib/StarDict/StarDict.h

@@ -32,7 +32,7 @@ class StarDict {
   struct DictzipInfo {
     uint32_t chunkLength = 0;  // Uncompressed chunk size (usually 58315)
     uint16_t chunkCount = 0;
-    uint32_t headerSize = 0;   // Total header size to skip
+    uint32_t headerSize = 0;         // Total header size to skip
     uint16_t* chunkSizes = nullptr;  // Array of compressed chunk sizes
     bool loaded = false;
   };