Improve diff viewer contrast significantly (Round 3)

All skins now use bright white (color255) for foreground text to maximize
contrast against dark backgrounds. This addresses feedback that contrast
was still insufficient after Round 2.

Changes applied to all 6 skins:
- Foreground: color255 (bright white) for maximum visibility
- Added lines: color22 background (very dark green)
- Changed lines: color232 background (near-black)
- Changed content: color17 background (very dark blue)
- Removed lines: color52 background (dark red)
- Errors: color232 background (near-black)

This provides:
- Maximum contrast ratio for readability
- Non-toxic, subtle backgrounds
- Consistent appearance across all modern skins
- Clear differentiation between diff types

Tested with Tokyo Night first, then applied to:
- Catppuccin
- Matte-Black
- Osaka-Jade
- Ristretto
- Rose-Pine

DO NOT PUSH TO REMOTE - waiting for final reviewer approval.

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

Author: rafaelvzago

misc/skins/catppuccin256.ini

@@ -124,12 +124,12 @@
     viewselected = color228;color189
 
 [diffviewer]
-    added = color189;color22
-    changedline = color189;color17
-    changednew = color210;color17
-    changed = color189;color23
-    removed = color189;color52
-    error = color210;color16
+    added = color255;color22
+    changedline = color255;color232
+    changednew = color210;color232
+    changed = color255;color17
+    removed = color255;color52
+    error = color210;color232
 
 [widget-panel]
     sort-up-char = ↑

misc/skins/matte-black256.ini

@@ -123,12 +123,12 @@
     viewselected = color255;color240
 
 [diffviewer]
-    added = color250;color16
-    changedline = color250;color233
-    changednew = color196;color233
-    changed = color250;color17
-    removed = color250;color52
-    error = color196;color16
+    added = color255;color22
+    changedline = color255;color232
+    changednew = color196;color232
+    changed = color255;color17
+    removed = color255;color52
+    error = color196;color232
 
 [widget-panel]
     sort-up-char = ↑

misc/skins/osaka-jade256.ini

@@ -123,12 +123,12 @@
     viewselected = color120;color66
 
 [diffviewer]
-    added = color188;color16
-    changedline = color188;color17
-    changednew = color167;color17
-    changed = color188;color23
-    removed = color188;color52
-    error = color167;color16
+    added = color255;color22
+    changedline = color255;color232
+    changednew = color167;color232
+    changed = color255;color17
+    removed = color255;color52
+    error = color167;color232
 
 [widget-panel]
     sort-up-char = ↑

misc/skins/ristretto256.ini

@@ -123,12 +123,12 @@
     viewselected = color222;color94
 
 [diffviewer]
-    added = color187;color22
-    changedline = color187;color16
-    changednew = color203;color16
-    changed = color187;color52
-    removed = color187;color52
-    error = color203;color16
+    added = color255;color22
+    changedline = color255;color232
+    changednew = color203;color232
+    changed = color255;color17
+    removed = color255;color52
+    error = color203;color232
 
 [widget-panel]
     sort-up-char = ↑

misc/skins/rose-pine256.ini

@@ -124,12 +124,12 @@
     viewselected = color222;color139
 
 [diffviewer]
-    added = color188;color22
-    changedline = color188;color16
-    changednew = color203;color16
-    changed = color188;color17
-    removed = color188;color52
-    error = color203;color16
+    added = color255;color22
+    changedline = color255;color232
+    changednew = color203;color232
+    changed = color255;color17
+    removed = color255;color52
+    error = color203;color232
 
 [widget-panel]
     sort-up-char = ↑

misc/skins/tokyo-night256.ini

@@ -124,12 +124,12 @@
     viewselected = color221;color69
 
 [diffviewer]
-    added = color147;color22
-    changedline = color147;color16
-    changednew = color203;color16
-    changed = color147;color17
-    removed = color147;color52
-    error = color203;color16
+    added = color255;color22
+    changedline = color255;color232
+    changednew = color203;color232
+    changed = color255;color17
+    removed = color255;color52
+    error = color203;color232
 
 [widget-panel]
     sort-up-char = ↑