feat: AI task API, token-based context windows, SSH password auth, sudo bypass detection

Replace message-count context windows with token-budget based ones for both
studio and shell. Add /api/ai/task endpoint for background tool
check/install/update. Enhance sudo blocking to catch piped/chained elevation
commands. Add SSH password support via sshpass and connection editing UI.
Remove realTokens persistence in favor of consumption tracking. Bump to 0.4.1.

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

internal/api/shell_conversation.go

@@ -79,10 +79,9 @@ type ShellMessage struct {
 }
 
 type ShellConvStore struct {
-	mu         sync.RWMutex
-	path       string
-	msgs       []ShellMessage
-	realTokens int
+	mu   sync.RWMutex
+	path string
+	msgs []ShellMessage
 }
 
 func NewShellConvStore() *ShellConvStore {
@@ -140,14 +139,10 @@ func (s *ShellConvStore) Clear() {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	s.msgs = []ShellMessage{}
-	s.realTokens = 0
 	s.save()
 }
 
 func (s *ShellConvStore) ApproxTokens() int {
-	if s.realTokens > 0 {
-		return s.realTokens
-	}
 	s.mu.RLock()
 	defer s.mu.RUnlock()
 	total := 0
@@ -161,16 +156,6 @@ func (s *ShellConvStore) ApproxTokens() int {
 	return total
 }
 
-// AddRealTokens accumulates actual token counts from the API response.
-func (s *ShellConvStore) AddRealTokens(tokens int) {
-	if tokens <= 0 {
-		return
-	}
-	s.mu.Lock()
-	s.realTokens += tokens
-	s.mu.Unlock()
-}
-
 func (s *ShellConvStore) AtLimit() bool {
 	return s.ApproxTokens() >= shellMaxTokens
 }