refactor(ux): simplify jargon and improve feature discoverability

Addressed P3 design opportunities from critique:

1. Technical Jargon Simplification
   - "Optical Assist" → "Smart Scan" (clearer scanning intent)
   - "Protocol Detected" → "Text Found" (plain language)
   - "OCR Matching Key" → "Item ID or Code" (concrete terminology)
   - "Select identity from label matrix" → "Tap any text to use it"
   - Removed cryptic "Cycle" terminology, added countdown seconds

2. Feature Discoverability
   - Added helpful descriptions to Admin manager sections
   - Scanner status message now hints at zoom and tap features
   - Concrete examples in input placeholders

3. Help & Documentation
   - User Management: "Create accounts and control access"
   - Category Groups: "Organize items by type or location"
   - Sign Out: clearer procedure description

Build: passes with zero errors

frontend/app/page.tsx

@@ -705,12 +705,12 @@ export default function Home() {
                        />
                     </div>
                     <div className="bg-slate-900/80 py-2.5 px-4 rounded-[1.2rem] border border-slate-800 focus-within:border-primary/50 transition-colors group">
-               <label className="text-xs text-slate-400 font-bold mb-0.5 block group-focus-within:text-primary transition-colors tracking-tight">OCR Matching Key</label>
+               <label className="text-xs text-slate-400 font-bold mb-0.5 block group-focus-within:text-primary transition-colors tracking-tight">Item ID or Code</label>
                        <textarea
                          value={editedItem.ocr_text || ''}
                          onChange={e => setEditedItem({ ...editedItem, ocr_text: e.target.value })}
                          className="w-full bg-slate-950 border border-slate-800 rounded-xl py-3 px-4 text-sm font-bold outline-none text-slate-400 resize-none h-12"
-                         placeholder="Paste identification string here..."
+                         placeholder="e.g., SKU-12345 or barcode text..."
                        />
                     </div>
                   </div>