Draw the borders of inactive windows in faint text

The borders of inactive windows are drawn in the terminal's default text
color, so they are as prominent as the text inside the windows. Draw
them in faint text instead. The terminal shades faint text toward its
background, so this works on dark and light backgrounds alike, and also
on backgrounds that are neither black nor white. The titles of inactive
windows use the same color, so they are dimmed too.

Terminals that don't support faint text draw the borders in the default
color, as before.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs-master/Config.md

@@ -181,7 +181,7 @@ gui:
 
     # Border color of non-focused windows
     inactiveBorderColor:
-      - default
+      - dim
 
     # Border color of focused window when searching in that window
     searchingActiveBorderColor:

pkg/config/user_config.go

@@ -893,7 +893,7 @@ func GetDefaultConfigForPlatform(platform string) *UserConfig {
 			Theme: ThemeConfig{
 				ActiveBorderColor:          []string{"green", "bold"},
 				SearchingActiveBorderColor: []string{"cyan", "bold"},
-				InactiveBorderColor:        []string{"default"},
+				InactiveBorderColor:        []string{"dim"},
 				OptionsTextColor:           []string{"blue"},
 				SelectedLineBgColor:        []string{"blue"},
 				CherryPickedCommitBgColor:  []string{"cyan"},

schema-master/config.json

@@ -739,7 +739,7 @@
               "uniqueItems": true,
               "description": "Border color of non-focused windows",
               "default": [
-                "default"
+                "dim"
               ]
             },
             "searchingActiveBorderColor": {