fix(ai): keep sidebar text readable in light theme

Use the dark AI panel text color for CLI question titles, usage totals
and tooltips, and small headings in chat and plans. Keep chat links on
the panel's blue accent instead of inheriting the editor theme color.

Verified the affected surfaces in the connected Linux app and compared
computed colors in light and dark themes. The full LESS build and
whitespace checks pass. All four fixes were reviewed in the running app.

Author: abose

src/styles/Extn-AIChatPanel.less

@@ -498,7 +498,7 @@
     gap: 12px;
     padding: 10px 12px;
     border-bottom: 1px solid rgba(128, 128, 128, 0.25);
-    h2 { margin: 0; font: inherit; font-weight: 600; overflow-wrap: anywhere; }
+    h2 { margin: 0; font: inherit; font-weight: 600; color: inherit; overflow-wrap: anywhere; }
 }
 .ai-rich-frame-heading { flex: 1; min-width: 0; }
 .ai-rich-frame-context { font-size: @ai-text-secondary; opacity: 0.65; margin-bottom: 4px; overflow-wrap: anywhere; }
@@ -2416,6 +2416,10 @@
             font-weight: 600;
         }
 
+        a {
+            color: #6b9eff;
+        }
+
         code {
             background-color: rgba(255, 255, 255, 0.08);
             color: @project-panel-text-1;
@@ -2485,7 +2489,7 @@
             color: @project-panel-text-2;
         }
 
-        h1, h2, h3, h4 {
+        h1, h2, h3, h4, h5, h6 {
             color: @project-panel-text-1;
             line-height: 1.25em;
         }
@@ -3999,7 +4003,7 @@
 
     // Heading top margin needs to be larger than paragraph margin so a
     // section header reads as a section header rather than another bullet.
-    h1, h2, h3, h4 {
+    h1, h2, h3, h4, h5, h6 {
         color: @project-panel-text-1;
         line-height: 1.25em;
     }
@@ -6707,6 +6711,7 @@
             font-size: @ai-text-body;
             font-weight: 600;
             font-variant-numeric: tabular-nums;
+            color: inherit;
         }
 
         span {
@@ -6922,6 +6927,7 @@
             font-size: @ai-text-body;
             font-weight: 600;
             font-variant-numeric: tabular-nums;
+            color: inherit;
         }
 
         span {