REDMINE_VERIFY=false / verify_ssl: false silently disabled TLS
certificate verification, exposing the connection to MITM attacks.
Config.validate() now prints a warning to stderr when verification
is disabled (exactly False; True or a CA-bundle path stays quiet).
validate() runs exactly once at CLI startup, so the warning is
emitted once per run and is visible in every scenario.
Closes#57
b624a8b8c2