fix: prevent package postinstall hang when generating jwt secret

The postinstall scripts generated the jwt secret with:

  cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 32 | head -n 1

This relies on SIGPIPE to terminate the infinite `cat /dev/urandom`
once `head` has read its single line. Inside a dpkg/apt maintainer-script
context the SIGPIPE disposition is not reliably delivered, so
`cat /dev/urandom` spins forever, the postinstall never returns, and the
whole `dpkg -i` / upgrade hangs.

Read a bounded 512 bytes with `head -c` instead so nothing depends on
SIGPIPE to terminate. 512 random bytes yield ~124 alphanumerics on
average, so the trailing `head -c 32` reliably produces a full 32-char
secret while staying dependency-free.

Fixes #2660

Author: kolaente

build/after-install-openrc.sh

@@ -2,7 +2,7 @@
 rc-update add vikunja default
 
 # Fix the config to contain proper values
-NEW_SECRET=$(cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 32 | head -n 1)
+NEW_SECRET=$(head -c 512 /dev/urandom | tr -dc 'a-zA-Z0-9' | head -c 32)
 sed -i "s/<jwt-secret>/$NEW_SECRET/g" /etc/vikunja/config.yml
 sed -i "s/<rootpath>/\/opt\/vikunja\//g" /etc/vikunja/config.yml
 sed -i "s/path: \"\.\/vikunja.db\"/path: \"\\/opt\/vikunja\/vikunja.db\"/g" /etc/vikunja/config.yml

build/after-install.sh

@@ -3,7 +3,7 @@
 systemctl enable vikunja.service
 
 # Fix the config to contain proper values
-NEW_SECRET=$(cat /dev/urandom | tr -dc 'a-zA-Z0-9' | fold -w 32 | head -n 1)
+NEW_SECRET=$(head -c 512 /dev/urandom | tr -dc 'a-zA-Z0-9' | head -c 32)
 sed -i "s/<jwt-secret>/$NEW_SECRET/g" /etc/vikunja/config.yml
 sed -i "s/<rootpath>/\/opt\/vikunja\//g" /etc/vikunja/config.yml
 sed -i "s/path: \"\.\/vikunja.db\"/path: \"\\/opt\/vikunja\/vikunja.db\"/g" /etc/vikunja/config.yml