feat: add 'ccs update' command with smart update notifications

Add comprehensive update functionality with intelligent notification system.
Supports manual update checking, automatic notifications every 24h, and works
across npm and direct installations with proper error handling.

Closes #12

scripts/completion/ccs.bash

@@ -18,7 +18,7 @@ _ccs_completion() {
 
   # Top-level completion (first argument)
   if [[ ${COMP_CWORD} -eq 1 ]]; then
-    local commands="auth doctor sync"
+    local commands="auth doctor sync update"
     local flags="--help --version --shell-completion -h -v -sc"
     local profiles=""