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>

CMakeLists.txt

@@ -1,6 +1,6 @@
 cmake_minimum_required(VERSION 3.21)
 
-project(OrbitHub VERSION 2026.9.16.5 LANGUAGES CXX)
+project(OrbitHub VERSION 2026.9.16.6 LANGUAGES CXX)
 
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)