Introduce opt-in booleans for task context and bmo nagging

dotfiles/bash/head.bashrc

@@ -2,6 +2,9 @@
 
 mkdir -p /var/tmp/bash-rv
 
+BASHUM_TASK_CTX=false
+BASHUM_BMO_NAG=false
+
 for include in \
   "${HOME}/.bash/colors.bashrc" \
   "${HOME}/.bash/defaults.bashrc" \

dotfiles/bash/post.bashrc

@@ -28,6 +28,7 @@ __bashum__save_rv() {
 }
 
 __bashum__task_context() {
+    $BASHUM_TASK_CTX || return 0
     local ctx       # TaskWarrior context
     type -t task >/dev/null || return 1
     ctx=$(task _get rc.context)
@@ -127,4 +128,4 @@ __bashum__setup_traps
 
 PROMPT_COMMAND=$(__bashum__mkpc)
 
-bmo nag
+$BASHUM_BMO_NAG && bmo nag