Make username/password connect prompts hard to miss (issue #22)

The inline prompt bar previously had no explicit styling and rendered
in the same color as the rest of the tab; a tab showing the prompt in
the background had no indication anything needed attention. The bar
now uses a solid QPalette::Highlight fill with HighlightedText for the
label and a hand-drawn contrasting badge, and a background tab gets a
"(Needs input)" title suffix plus a distinct tab-bar color.

A first pass at the tab color (#6a1b9a) was reported unreadable in
dark mode; replaced with #ab47bc, tuned to match the visibility of the
existing connection-state colors.

Bump version to v2026.9.16.6.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/session_tab.h

@@ -67,10 +67,16 @@ public:
     bool supportsVncScaleToggle() const;
     void setVncScaleToFit(bool scaleToFit);
     bool vncScaleToFit() const;
+    bool awaitingUserInput() const;
 
 signals:
     void tabTitleChanged(const QString& title);
     void tabStateChanged(SessionState state);
+    // Fires whenever the inline username/password prompt bar is shown or
+    // hidden -- independent of tabStateChanged(), since the backend is
+    // still just "Connecting" while it's up. Lets SessionWindow mark a
+    // background tab that needs the user's attention (issue #22).
+    void awaitingUserInputChanged(bool waiting);
     void terminalThemeChanged(const QString& themeName);
     void terminalFontSizeChanged(int pointSize);
     void eventsPanelVisibilityChanged(bool expanded);
@@ -129,11 +135,13 @@ private:
     QToolButton* m_exportEventsButton;
     QWidget* m_eventsPanel;
     QWidget* m_passwordPromptBar;
+    QLabel* m_passwordPromptIcon;
     QLabel* m_passwordPromptLabel;
     QLineEdit* m_passwordPromptInput;
     QPushButton* m_passwordPromptConnectButton;
     QPushButton* m_passwordPromptCancelButton;
     std::function<void(std::optional<QString>)> m_passwordPromptCallback;
+    bool m_awaitingUserInput;
     enum class EventSeverity {
         Info,
         Warning,