Remember window and tab; fill saved passwords; match the title bar

The window's position and size survive a restart, and so does the app
you were last in.

Saving a password was only half of it - a saved password you cannot get
back out is not saved in any useful sense. Right-click now offers "Fill
saved password" wherever a page has a password field. Only on an explicit
click, only for the host on screen, and only into that page's own fields,
never on load. The value is set through the native setter and followed by
input and change events, because assigning .value is invisible to React
and Angular and the site would submit an empty field.

The title bar is painted the nav's colour rather than its own grey, so
the two read as one surface in either theme. Doing that revealed that the
window's content had always run the full height underneath it - the
opaque bar was hiding it - so the shell is now inset by the measured
title bar height, or the nav lands on the traffic lights.

The rail's unread badge is a fixed circle inside the button's bounds.
Padding around a number made a pill at two digits, and hanging it off the
corner put it under the rail's clip; past nine it reads "9+", with the
figure itself in the expanded nav.

src-tauri/gen/schemas/capabilities.json

@@ -1 +1 @@
-{"default":{"identifier":"default","description":"The shell webview. App webviews are deliberately absent: remote content gets no IPC.","local":true,"windows":["main"],"permissions":["core:default","core:window:allow-start-dragging","opener:default","notification:default"]}}
+{"default":{"identifier":"default","description":"The shell webview. App webviews are deliberately absent: remote content gets no IPC.","local":true,"windows":["main"],"permissions":["core:default","core:window:allow-start-dragging","opener:default","notification:default","window-state:default"]}}