fix: support Tailwind opacity modifiers with CSS variable accent colors

The accent colors were changed from hardcoded hex to CSS variables for
per-campaign theming, but Tailwind v3 cannot decompose var() values to
apply opacity modifiers (/20, /10, etc.), breaking all @apply directives
using accent/{opacity} (16 occurrences).

Fix: add parallel --color-accent-rgb CSS custom properties holding
space-separated RGB channels. Tailwind config uses these with the
<alpha-value> placeholder for opacity support. Raw CSS/JS continues
using the hex-based --color-accent variables unchanged.

https://claude.ai/code/session_01WJEjfBqjZaGatHiXXXDupo

Author: claude

static/css/input.css

@@ -37,6 +37,10 @@
     --color-accent:        #6366f1;  /* indigo-500 */
     --color-accent-hover:  #4f46e5;  /* indigo-600 -- darker for hover states */
     --color-accent-light:  #a5b4fc;  /* indigo-300 -- lighter for badges/tags */
+    /* RGB channel variants for Tailwind opacity modifier support (<alpha-value>). */
+    --color-accent-rgb:       99 102 241;
+    --color-accent-hover-rgb: 79 70 229;
+    --color-accent-light-rgb: 165 180 252;
     --color-sidebar-bg:    #1a1c23;  /* always dark */
   }
 
@@ -57,6 +61,9 @@
     --color-accent:        #6366f1;  /* indigo-500 -- same both modes */
     --color-accent-hover:  #4f46e5;  /* indigo-600 */
     --color-accent-light:  #a5b4fc;  /* indigo-300 */
+    --color-accent-rgb:       99 102 241;
+    --color-accent-hover-rgb: 79 70 229;
+    --color-accent-light-rgb: 165 180 252;
     --color-sidebar-bg:    #1a1c23;  /* always dark */
   }
 
@@ -83,7 +90,7 @@
   }
   .btn-primary {
     @apply btn bg-accent text-white hover:bg-accent-hover
-           focus:ring-accent shadow-sm hover:shadow-md hover:shadow-indigo-500/20;
+           focus:ring-accent shadow-sm hover:shadow-md hover:shadow-accent/20;
   }
   .btn-secondary {
     @apply btn bg-surface text-fg-body hover:bg-surface-alt
@@ -845,7 +852,7 @@
 
   /* Reorg mode active indicator on toggle button. */
   #sidebar-reorg-toggle.bg-accent\/20 {
-    background-color: rgba(var(--color-accent-rgb, 99, 102, 241), 0.2);
+    background-color: rgb(var(--color-accent-rgb, 99 102 241) / 0.2);
   }
 
   /* Tree toggle button styling. */

tailwind.config.js

@@ -40,9 +40,9 @@ module.exports = {
         // Accent color for links, buttons, active states.
         // References CSS custom property so per-campaign overrides work.
         accent: {
-          DEFAULT: 'var(--color-accent, #6366f1)',
-          hover: 'var(--color-accent-hover, #4f46e5)',
-          light: 'var(--color-accent-light, #a5b4fc)',
+          DEFAULT: 'rgb(var(--color-accent-rgb, 99 102 241) / <alpha-value>)',
+          hover: 'rgb(var(--color-accent-hover-rgb, 79 70 229) / <alpha-value>)',
+          light: 'rgb(var(--color-accent-light-rgb, 165 180 252) / <alpha-value>)',
         },
 
         // ── Semantic theme tokens ──────────────────────────────