fix: strip leading 'v' from version in build-deb.sh unconditionally

Debian versions must start with a digit. When called via 'make deb',
VERSION is passed from Makefile (git describe output includes 'v' prefix).
The strip was previously only done inside the auto-detection branch,
so 'make deb' produced invalid versions like 'v2026.07.30-2-g05604a8-1'.

Now VERSION= runs after the version is determined, regardless
of whether it came from an argument or auto-detection.

scripts/build-deb.sh

@@ -7,9 +7,10 @@ ARCH="${2:-$(dpkg --print-architecture 2>/dev/null || echo "amd64")}"
 
 if [[ -z "$VERSION" ]]; then
     VERSION=$(git describe --tags --always --dirty 2>/dev/null || echo "dev")
-    VERSION="${VERSION#v}"
 fi
 
+VERSION="${VERSION#v}"
+
 if ! command -v dpkg-deb &>/dev/null; then
     echo "Error: dpkg-deb not found. Install with: sudo apt install dpkg" >&2
     exit 1