Further reduce diff viewer background vibrancy (Round 2)

Addressed reviewer feedback that backgrounds were still too vibrant/toxic.
Used much darker, more subtle backgrounds (color16-23 range) to eliminate
the toxic appearance while maintaining good contrast.

Changes per skin:
- Catppuccin: Now uses color22 (very dark green) and color17 (very dark blue)
- Matte-Black: Uses color16 (black) and color233 (very dark gray)
- Tokyo-Night: Uses color16 (black) and color22 (very dark green)
- Osaka-Jade: Uses color16 (black) and color23 (dark teal)
- Ristretto: Uses color16 (black) and color22 (very dark green)
- Rose-Pine: Uses color16 (black) and color17 (very dark blue)

All backgrounds now stay below color60 to avoid any mid-range brightness.
Text remains clearly readable with high contrast on these dark backgrounds.
Theme identity is preserved through subtle color tinting.

DO NOT PUSH TO REMOTE - waiting for reviewer feedback on local changes.

Signed-off-by: Rafael Zago <rafaelvzago@gmail.com>

Author: rafaelvzago

misc/skins/catppuccin256.ini

@@ -124,12 +124,12 @@
     viewselected = color228;color189
 
 [diffviewer]
-    added = color234;color108
-    changedline = color189;color24
-    changednew = color210;color24
-    changed = color189;color60
-    removed = color234;color131
-    error = color210;color234
+    added = color189;color22
+    changedline = color189;color17
+    changednew = color210;color17
+    changed = color189;color23
+    removed = color189;color52
+    error = color210;color16
 
 [widget-panel]
     sort-up-char = ↑

misc/skins/matte-black256.ini

@@ -123,12 +123,12 @@
     viewselected = color255;color240
 
 [diffviewer]
-    added = color250;color22
-    changedline = color250;color238
-    changednew = color196;color238
-    changed = color250;color24
+    added = color250;color16
+    changedline = color250;color233
+    changednew = color196;color233
+    changed = color250;color17
     removed = color250;color52
-    error = color196;color235
+    error = color196;color16
 
 [widget-panel]
     sort-up-char = ↑

misc/skins/osaka-jade256.ini

@@ -123,12 +123,12 @@
     viewselected = color120;color66
 
 [diffviewer]
-    added = color234;color29
-    changedline = color188;color23
-    changednew = color167;color23
-    changed = color188;color30
-    removed = color234;color88
-    error = color167;color234
+    added = color188;color16
+    changedline = color188;color17
+    changednew = color167;color17
+    changed = color188;color23
+    removed = color188;color52
+    error = color167;color16
 
 [widget-panel]
     sort-up-char = ↑

misc/skins/ristretto256.ini

@@ -123,12 +123,12 @@
     viewselected = color222;color94
 
 [diffviewer]
-    added = color234;color58
-    changedline = color187;color52
-    changednew = color203;color52
-    changed = color187;color94
-    removed = color234;color88
-    error = color203;color234
+    added = color187;color22
+    changedline = color187;color16
+    changednew = color203;color16
+    changed = color187;color52
+    removed = color187;color52
+    error = color203;color16
 
 [widget-panel]
     sort-up-char = ↑

misc/skins/rose-pine256.ini

@@ -124,12 +124,12 @@
     viewselected = color222;color139
 
 [diffviewer]
-    added = color234;color65
-    changedline = color188;color53
-    changednew = color203;color53
-    changed = color188;color60
-    removed = color234;color88
-    error = color203;color234
+    added = color188;color22
+    changedline = color188;color16
+    changednew = color203;color16
+    changed = color188;color17
+    removed = color188;color52
+    error = color203;color16
 
 [widget-panel]
     sort-up-char = ↑

misc/skins/tokyo-night256.ini

@@ -124,12 +124,12 @@
     viewselected = color221;color69
 
 [diffviewer]
-    added = color234;color108
-    changedline = color147;color17
-    changednew = color203;color17
-    changed = color147;color24
-    removed = color234;color131
-    error = color203;color234
+    added = color147;color22
+    changedline = color147;color16
+    changednew = color203;color16
+    changed = color147;color17
+    removed = color147;color52
+    error = color203;color16
 
 [widget-panel]
     sort-up-char = ↑