fix: use standard theme variables in device-flow and popup CSS

Author: euxx

src/popup/popup.css

@@ -505,7 +505,7 @@ body.dark-theme .pat-input.input-error {
 
 .repo-mark-read-btn:hover {
   background: var(--bg-secondary);
-  color: var(--accent-color);
+  color: var(--text-primary);
 }
 
 .repo-mark-read-btn:active {

src/styles/device-flow.css

@@ -28,7 +28,7 @@ body {
 }
 
 .logo {
-  color: var(--color-primary);
+  color: var(--text-primary);
   margin-bottom: 20px;
 }
 
@@ -45,7 +45,7 @@ p {
 
 .device-code-display {
   background: var(--bg-primary);
-  border: 2px solid var(--color-primary);
+  border: 1px solid var(--border-color);
   border-radius: var(--radius-sm);
   padding: 20px;
   margin-bottom: 24px;
@@ -56,7 +56,7 @@ p {
   font-size: 24px;
   font-weight: 700;
   letter-spacing: 4px;
-  color: var(--color-primary);
+  color: var(--text-primary);
   display: block;
   margin-bottom: 14px;
 }
@@ -74,25 +74,25 @@ p {
 
 .copy-btn:hover {
   background: var(--bg-hover);
-  border-color: var(--color-primary);
+  border-color: var(--text-tertiary);
 }
 
 .btn-primary {
-  background: var(--color-primary);
-  color: white;
-  border: none;
+  background: var(--bg-hover);
+  color: var(--text-primary);
+  border: 1px solid var(--border-color);
   border-radius: var(--radius-sm);
   padding: 12px 24px;
   font-size: 16px;
-  font-weight: 500;
+  font-weight: 600;
   cursor: pointer;
   transition: all 0.2s;
   width: 100%;
   margin-bottom: 16px;
 }
 
 .btn-primary:hover {
-  background: var(--color-primary-hover);
+  background: var(--border-color);
 }
 
 .btn-primary:disabled {
@@ -104,7 +104,6 @@ p {
   margin: 16px 0;
   padding: 10px 12px;
   background: var(--bg-primary);
-  border-left: 3px solid var(--color-primary);
   border-radius: var(--radius-sm);
   font-size: 13px;
   line-height: 1.4;
@@ -138,7 +137,7 @@ p {
   width: 16px;
   height: 16px;
   border: 2px solid var(--text-tertiary);
-  border-top-color: var(--color-primary);
+  border-top-color: var(--text-secondary);
   border-radius: 50%;
   animation: spin 1s linear infinite;
   margin-right: 6px;

src/styles/variables.css

@@ -6,7 +6,6 @@
 :root {
   /* Theme Colors - Monochrome */
   --primary-color: #1f2937;
-  --primary-hover: #111827;
 
   /* UI Colors */
   --text-primary: #1f2937;
@@ -35,7 +34,6 @@
 /* Dark Theme - GitHub Notifications Style */
 body.dark-theme {
   --primary-color: #d1d5db;
-  --primary-hover: #9ca3af;
 
   --text-primary: #adbac7;
   --text-secondary: #768390;