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.

.gitea/workflows/ci.yml

@@ -33,5 +33,9 @@ jobs:
             echo "clang-format not found, skipping format check"
           fi
 
+      - name: Generate Dictionary Index
+        run: |
+          python3 scripts/generate_dict_index.py --zip dict-en-en.zip --output lib/StarDict/DictPrefixIndex.generated.h
+
       - name: Build CrossPoint
         run: pio run