chore: cleanup — .gitignore, track design docs

.gitignore

@@ -1,5 +1,6 @@
 # Generated from version.txt
 src/version.h
+android/app/src/main/java/nl/eddydevink/sylda/SylDaVersions.kt
 
 # PlatformIO
 .pio/
@@ -46,4 +47,18 @@ codereview.md
 DC3-24V*.md
 DC3-24V*.pdf
 esplibalternatief.md
+docs/handleiding.md
 release/
+releases/
+
+# Test/debug firmware files
+src/blink.cpp
+src/c1.cpp
+src/get_mac.cpp
+src/min_cli.cpp
+src/min_srv.cpp
+src/s1.cpp
+src/test_*.cpp
+
+# Python cache
+scripts/__pycache__/