ci: add version consistency check and fully automate release pipeline

- New tools/check_versions.sh: verifies version.txt, version.h, SylDaVersions.kt match
- release.yml: 'Verify version consistency' step after build, aborts release if mismatch
- ci.yml: same check after debug APK build
- scripts/release.sh: now runs full pipeline (pio run -> copy firmware -> gradle -> check)
  and refuses dirty working tree
- Untrack version.h, SylDaVersions.kt, release/ — always regenerated fresh from version.txt

Prevents the v1.1 bug where stale generated files caused version mismatch
and infinite re-flash loop.

android/app/src/main/java/nl/eddydevink/sylda/SylDaVersions.kt

@@ -1,7 +0,0 @@
-// Auto-generated from version.txt — DO NOT EDIT
-package nl.eddydevink.sylda
-
-object SylDaVersions {
-    const val SERVER = "17"
-    const val CLIENT = "3"
-}