fix: simplify BNC binary detection and handle Qt5 package variations

[jajera]

Closes #115

Problem

1. Binary detection failed — the extracted bnc-2.13.6 file has no exec bit set, so find -perm /111 misses it, and the subshell fallback loses the result.
2. Qt5 package names differ across distros (Fedora has qt5-qtbase only, no qt5-qtbase-gui; Debian uses libqt5core5a; newer Ubuntu uses libqt5core5t64). The script was failing hard on unresolved package names.

Fix

• Use direct path $TMP_DIR/bnc/bnc-${BNC_VERSION} as primary detection (we know the naming convention)
• Use fallback chains (|| true) for Qt5 package install so missing package names don't abort the script
• Added support for apk (Alpine) and multiple Debian/Ubuntu naming variants