feat(06-02): replace EmojiPicker with IconPicker across all category components

- CategoryPicker shows LucideIcon prefix and uses IconPicker for inline create
- CategoryHeader displays LucideIcon in view mode and IconPicker in edit mode
- OnboardingWizard uses IconPicker for category creation step
- CreateThreadModal drops emoji from category select options
- Fixed categoryEmoji -> categoryIcon in routes and useCategories hook

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/client/components/OnboardingWizard.tsx

@@ -2,6 +2,7 @@ import { useState } from "react";
 import { useCreateCategory } from "../hooks/useCategories";
 import { useCreateItem } from "../hooks/useItems";
 import { useUpdateSetting } from "../hooks/useSettings";
+import { IconPicker } from "./IconPicker";
 
 interface OnboardingWizardProps {
   onComplete: () => void;
@@ -12,7 +13,7 @@ export function OnboardingWizard({ onComplete }: OnboardingWizardProps) {
 
   // Step 2 state
   const [categoryName, setCategoryName] = useState("");
-  const [categoryEmoji, setCategoryEmoji] = useState("");
+  const [categoryIcon, setCategoryIcon] = useState("");
   const [categoryError, setCategoryError] = useState("");
   const [createdCategoryId, setCreatedCategoryId] = useState<number | null>(null);
 
@@ -41,7 +42,7 @@ export function OnboardingWizard({ onComplete }: OnboardingWizardProps) {
     }
     setCategoryError("");
     createCategory.mutate(
-      { name, emoji: categoryEmoji.trim() || undefined },
+      { name, icon: categoryIcon.trim() || undefined },
       {
         onSuccess: (created) => {
           setCreatedCategoryId(created.id);
@@ -164,20 +165,13 @@ export function OnboardingWizard({ onComplete }: OnboardingWizardProps) {
               </div>
 
               <div>
-                <label
-                  htmlFor="onboard-cat-emoji"
-                  className="block text-sm font-medium text-gray-700 mb-1"
-                >
-                  Emoji (optional)
+                <label className="block text-sm font-medium text-gray-700 mb-1">
+                  Icon (optional)
                 </label>
-                <input
-                  id="onboard-cat-emoji"
-                  type="text"
-                  value={categoryEmoji}
-                  onChange={(e) => setCategoryEmoji(e.target.value)}
-                  className="w-20 px-3 py-2 border border-gray-200 rounded-lg text-center text-lg focus:outline-none focus:ring-2 focus:ring-blue-500 focus:border-transparent"
-                  placeholder="&#9978;"
-                  maxLength={4}
+                <IconPicker
+                  value={categoryIcon}
+                  onChange={setCategoryIcon}
+                  size="md"
                 />
               </div>