feat(phase7.1): add HelpTooltip system with contextual help icons

- New HelpTooltip component: hover-triggered floating panel, themed via
  CSS variables, supports top/right/bottom/left positioning, no deps
- New helpTexts.ts registry: 14 entries covering render settings,
  admin actions, template fields, and wizard fields
- Admin.tsx: tooltips on Cycles/EEVEE samples, smooth angle, regenerate
  thumbnails, process unprocessed
- RenderTemplateTable.tsx: tooltips on material replace, lighting only,
  shadow catcher column headers

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/admin/RenderTemplateTable.tsx

@@ -1,6 +1,7 @@
 import { useState, useRef } from 'react'
 import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query'
 import { Pencil, Trash2, Plus, Check, X, Upload, Download } from 'lucide-react'
+import HelpTooltip from '../HelpTooltip'
 import { toast } from 'sonner'
 import {
   listRenderTemplates,
@@ -165,9 +166,24 @@ export default function RenderTemplateTable() {
               <th className="px-3 py-2 font-medium">Category</th>
               <th className="px-3 py-2 font-medium">Output Type</th>
               <th className="px-3 py-2 font-medium">Collection</th>
-              <th className="px-3 py-2 font-medium">Mat. Replace</th>
-              <th className="px-3 py-2 font-medium">Lighting Only</th>
-              <th className="px-3 py-2 font-medium" title="Enable Shadowcatcher collection (Cycles only)">Shadow Catcher</th>
+              <th className="px-3 py-2 font-medium">
+                <span className="inline-flex items-center gap-1">
+                  Mat. Replace
+                  <HelpTooltip helpKey="template.material_replace_enabled" position="bottom" size={12} />
+                </span>
+              </th>
+              <th className="px-3 py-2 font-medium">
+                <span className="inline-flex items-center gap-1">
+                  Lighting Only
+                  <HelpTooltip helpKey="template.lighting_only" position="bottom" size={12} />
+                </span>
+              </th>
+              <th className="px-3 py-2 font-medium">
+                <span className="inline-flex items-center gap-1">
+                  Shadow Catcher
+                  <HelpTooltip helpKey="template.shadow_catcher" position="bottom" size={12} />
+                </span>
+              </th>
               <th className="px-3 py-2 font-medium" title="Rotate camera around product instead of product rotation (faster GPU rendering)">Cam Orbit</th>
               <th className="px-3 py-2 font-medium">.blend File</th>
               <th className="px-3 py-2 font-medium">Active</th>