refactor: replace hardcoded blue with dynamic accent color variable

Replace direct `--color-blue` references with new `--interactive-accent-blue` variable that blends interactive accent with blue, enabling consistent theme-aware styling across edit mode UI elements.

Components/ChatArea.svelte

@@ -321,6 +321,7 @@
   {/each}
 
   <ChatAreaThought bind:thoughtElement thought={currentThought}/>
+  <StreamingIndicator bind:streamingElement editModeActive={editModeActive}/>
   {#if isSubmitting}
     <StreamingIndicator bind:streamingElement editModeActive={editModeActive}/>
   {/if}

Components/ChatWindow.svelte

@@ -250,7 +250,7 @@
   }
 
   #input-container.edit-mode {
-    border-color: var(--color-blue);
+    border-color: var(--interactive-accent-blue);
     transition: border-color 0.5s ease-out;
   }
 
@@ -276,8 +276,8 @@
   }
   
   #input-field.edit-mode:focus {
-    border-color: var(--color-blue);
-    box-shadow: 0px 0px 3px 1px var(--color-blue);
+    border-color: var(--interactive-accent-blue);
+    box-shadow: 0px 0px 3px 1px var(--interactive-accent-blue);
     transition: border-color 0.5s ease-out;
   }
 
@@ -317,7 +317,7 @@
   }
 
   #submit-button.edit-mode {
-    background-color: var(--color-blue);
+    background-color: var(--interactive-accent-blue);
   }
 
   #submit-button:not(:disabled):hover {

Components/StreamingIndicator.svelte

@@ -31,7 +31,7 @@
   }
 
   .container.edit-mode {
-    --streaming-color: var(--color-blue);
+    --streaming-color: var(--interactive-accent-blue);
   }
 
   .📦 {

styles.css

@@ -100,6 +100,10 @@
 /* CSS Variables for Theming */
 /* ============================== */
 
+body {
+  --interactive-accent-blue: color-mix(in srgb, var(--interactive-accent) 50%, var(--color-blue) 50%);
+}
+
 :root {
   --code-background: #24292e;
   --code-background-inline: rgba(27, 31, 35, 0.05);