commands: Fix --panicOnWarning flag having no effect with module version warnings

The --panicOnWarning flag was not wired into the root command's logger,
so warnings emitted during config loading (such as module version
incompatibility warnings) would not trigger a panic.

Bind the panicOnWarning flag to the rootCommand struct and set the
PanicOnWarningHook on the logger created in createLogger.

Fixes #14524

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

testscripts/commands/hugo__paniconwarning_mod.txt

@@ -0,0 +1,13 @@
+! hugo --panicOnWarning
+
+stderr 'is not compatible with this Hugo'
+
+-- hugo.toml --
+baseURL="https://example.org"
+
+[module]
+[module.hugoVersion]
+min = "0.148.0"
+max = "0.148.0"
+-- layouts/all.html --
+All.