fix: restore dark HC contrast for emphasis, attention, severe, and success tokens

All 4 failures were introduced by calibrating dark HC base color steps
to red's luminance profile, which moved mid-range steps from dark to
medium-brightness, breaking fg/bg pair relationships.

Fixes:
- display-blue-bgColor-emphasis: blue.4 -> blue.2 in all dark HC variants
  (all other hues already used step 2; blue used step 4 only because
  old uncalibrated steps 1-4 were all identical, accidentally passing)
- fgColor-success (colorblind/tritanopia HC): blue.8 -> blue.9
  (blue.8 got dimmer, blue.5 muted bg got brighter = less contrast)
- fgColor-attention (dark HC variants): add yellow.9 override
  (no dark HC override existed; inherited yellow.8 which got dimmer)
- fgColor-severe (dark HC): orange.8 -> orange.9, red.8 -> red.9
  (tritanopia uses red for severe; both got dimmer from calibration)

Author: lukasoppermann

src/tokens/functional/color/display.json5

@@ -182,16 +182,16 @@
                 $value: '{base.color.blue.9}',
               },
               'dark-high-contrast': {
-                $value: '{base.color.blue.4}',
+                $value: '{base.color.blue.2}',
               },
               'dark-dimmed-high-contrast': {
-                $value: '{base.color.blue.4}',
+                $value: '{base.color.blue.2}',
               },
               'dark-protanopia-deuteranopia-high-contrast': {
-                $value: '{base.color.blue.4}',
+                $value: '{base.color.blue.2}',
               },
               'dark-tritanopia-high-contrast': {
-                $value: '{base.color.blue.4}',
+                $value: '{base.color.blue.2}',
               },
             },
           },

src/tokens/functional/color/fgColor.json5

@@ -255,11 +255,11 @@
           'dark-dimmed-high-contrast': '{base.color.green.11}',
           'light-high-contrast': '#04591f', /* Custom hex between green.5 and green.6: level 5 fails 7:1 vs bgColor-muted, level 6 is too dark to visually differentiate status colors. Same approach as dark HC overrides (PR #1190). */
           'dark-protanopia-deuteranopia': '{base.color.blue.7}',
-          'dark-protanopia-deuteranopia-high-contrast': '{base.color.blue.8}',
+          'dark-protanopia-deuteranopia-high-contrast': '{base.color.blue.9}',
           'light-protanopia-deuteranopia': '{base.color.blue.7}',
           'light-protanopia-deuteranopia-high-contrast': '{base.color.blue.8}',
           'dark-tritanopia': '{base.color.blue.7}',
-          'dark-tritanopia-high-contrast': '{base.color.blue.8}',
+          'dark-tritanopia-high-contrast': '{base.color.blue.9}',
           'light-tritanopia': '{base.color.blue.7}',
           'light-tritanopia-high-contrast': '{base.color.blue.8}',
         },
@@ -313,6 +313,9 @@
         },
         'org.primer.overrides': {
           dark: '{base.color.yellow.8}',
+          'dark-high-contrast': '{base.color.yellow.9}',
+          'dark-protanopia-deuteranopia-high-contrast': '{base.color.yellow.9}',
+          'dark-tritanopia-high-contrast': '{base.color.yellow.9}',
           'light-high-contrast': '{base.color.yellow.8}',
           'light-protanopia-deuteranopia-high-contrast': '{base.color.yellow.8}',
           'light-tritanopia-high-contrast': '{base.color.yellow.8}',
@@ -339,12 +342,12 @@
         },
         'org.primer.overrides': {
           dark: '{base.color.orange.7}',
-          'dark-high-contrast': '{base.color.orange.8}',
+          'dark-high-contrast': '{base.color.orange.9}',
           'dark-dimmed-high-contrast': '{base.color.orange.10}',
-          'dark-protanopia-deuteranopia-high-contrast': '{base.color.orange.8}',
+          'dark-protanopia-deuteranopia-high-contrast': '{base.color.orange.9}',
           'light-high-contrast': '{base.color.orange.8}',
           'dark-tritanopia': '{base.color.red.7}',
-          'dark-tritanopia-high-contrast': '{base.color.red.8}',
+          'dark-tritanopia-high-contrast': '{base.color.red.9}',
           'light-tritanopia': '{base.color.red.7}',
           'light-tritanopia-high-contrast': '{base.color.red.8}',
           'light-protanopia-deuteranopia-high-contrast': '{base.color.orange.8}',