feat(09-03): apply MD3 button styles and elevation across all wizard steps

- BackendCard: rounded-lg -> rounded-xl, added shadow/shadow-md elevation
- OutputBlock: pre rounded -> rounded-xl + shadow-sm; Copy/Download use MD3_BTN_OUTLINED small variant
- BackendSelectionStep: added explicit Next submit button with MD3_BTN_FILLED
- RemoteConfigStep: Back uses MD3_BTN_OUTLINED, Next uses MD3_BTN_FILLED
- DeploymentStep: Back uses MD3_BTN_OUTLINED, Next/Review uses MD3_BTN_FILLED
- ReviewStep: Back uses MD3_BTN_OUTLINED, Download All (ZIP) uses MD3_BTN_FILLED
- All 179 tests pass (zero regressions)

src/components/ui/BackendCard.tsx

@@ -14,10 +14,10 @@ export function BackendCard({ name, description, selected = false, onClick, ...r
       onClick={onClick}
       data-selected={selected}
       className={[
-        'flex flex-col items-start gap-1 rounded-lg border-2 p-4 text-left transition-colors',
+        'flex flex-col items-start gap-1 rounded-xl border-2 p-4 text-left transition-all',
         selected
-          ? 'border-primary bg-primary/10'
+          ? 'border-primary bg-primary/10 shadow-md'
-          : 'border-outline bg-surface-container hover:border-primary hover:bg-surface',
+          : 'border-outline bg-surface-container shadow hover:border-primary hover:bg-surface hover:shadow-md',
       ].join(' ')}
       {...rest}
     >

src/components/wizard/BackendSelectionStep.tsx

@@ -6,6 +6,7 @@ import { useWizard } from '../../store/context';
 import type { BackendType } from '../../store/types';
 import { BACKEND_REGISTRY } from '../../schemas/registry';
 import { BackendCard } from '../ui/BackendCard';
+import { MD3_BTN_FILLED } from '../../styles/md3-buttons';
 
 const remoteNameSchema = z.object({
   name: z
@@ -71,6 +72,11 @@ export function BackendSelectionStep() {
             />
           ))}
         </div>
+        <div className="flex gap-3 mt-6">
+          <button type="submit" className={MD3_BTN_FILLED}>
+            Next
+          </button>
+        </div>
       </form>
     </div>
   );

src/components/wizard/DeploymentStep.tsx

@@ -3,6 +3,7 @@
 // Dispatches SET_DEPLOYMENT live on every control change (no submit needed for deployment options).
 
 import { useWizard } from '../../store/context';
+import { MD3_BTN_FILLED, MD3_BTN_OUTLINED } from '../../styles/md3-buttons';
 
 export function DeploymentStep() {
   const { state, dispatch } = useWizard();
@@ -91,14 +92,14 @@ export function DeploymentStep() {
         <button
           type="button"
           onClick={() => dispatch({ type: 'SET_STEP', payload: 1 })}
-          className="px-4 py-2 text-sm border border-outline rounded-md hover:bg-surface"
+          className={MD3_BTN_OUTLINED}
         >
           Back
         </button>
         <button
           type="button"
           onClick={() => dispatch({ type: 'SET_STEP', payload: 3 })}
-          className="px-4 py-2 text-sm bg-primary text-on-primary rounded-md hover:bg-primary"
+          className={MD3_BTN_FILLED}
         >
           Next / Review
         </button>

src/components/wizard/OutputBlock.tsx

@@ -3,6 +3,7 @@
 // disabled prop gates both actions (SECU-01 security acknowledgement gate).
 import { useState } from 'react';
 import { downloadFile } from '../../utils/downloadFile';
+import { MD3_BTN_OUTLINED } from '../../styles/md3-buttons';
 
 export interface OutputBlockProps {
   label: string;
@@ -20,6 +21,8 @@ export function OutputBlock({ label, content, filename, disabled = false }: Outp
     setTimeout(() => setCopied(false), 2000);
   }
 
+  const smallBtn = `${MD3_BTN_OUTLINED} !text-xs !px-3 !py-1.5`;
+
   return (
     <div className="mb-6">
       <div className="flex items-center justify-between mb-1">
@@ -29,7 +32,7 @@ export function OutputBlock({ label, content, filename, disabled = false }: Outp
             type="button"
             disabled={disabled}
             onClick={handleCopy}
-            className="text-xs px-2 py-1 rounded border border-outline disabled:opacity-40"
+            className={smallBtn}
           >
             {copied ? 'Copied!' : 'Copy'}
           </button>
@@ -38,14 +41,14 @@ export function OutputBlock({ label, content, filename, disabled = false }: Outp
               type="button"
               disabled={disabled}
               onClick={() => downloadFile(content, filename)}
-              className="text-xs px-2 py-1 rounded border border-outline disabled:opacity-40"
+              className={smallBtn}
             >
               Download
             </button>
           )}
         </div>
       </div>
-      <pre className="bg-surface-variant text-on-surface-variant rounded p-4 text-xs overflow-x-auto whitespace-pre-wrap">
+      <pre className="bg-surface-variant text-on-surface-variant rounded-xl shadow-sm p-4 text-xs overflow-x-auto whitespace-pre-wrap">
         <code>{content}</code>
       </pre>
     </div>

src/components/wizard/RemoteConfigStep.tsx

@@ -11,6 +11,7 @@ import { FieldRenderer } from '../ui/FieldRenderer';
 import { AzureAuthToggle } from './AzureAuthToggle';
 import { SftpAuthToggle } from './SftpAuthToggle';
 import type { FieldError } from 'react-hook-form';
+import { MD3_BTN_FILLED, MD3_BTN_OUTLINED } from '../../styles/md3-buttons';
 
 export function RemoteConfigStep() {
   const { state, dispatch } = useWizard();
@@ -110,13 +111,13 @@ export function RemoteConfigStep() {
           <button
             type="button"
             onClick={() => dispatch({ type: 'SET_STEP', payload: 0 })}
-            className="px-4 py-2 text-sm border border-outline rounded-md hover:bg-surface"
+            className={MD3_BTN_OUTLINED}
           >
             Back
           </button>
           <button
             type="submit"
-            className="px-4 py-2 text-sm bg-primary text-on-primary rounded-md hover:bg-primary"
+            className={MD3_BTN_FILLED}
           >
             Next
           </button>

src/components/wizard/ReviewStep.tsx

@@ -3,6 +3,7 @@
 // Covers CONF-02, CONF-03, DOWN-01–DOWN-06, SECU-01, SECU-02.
 import { useMemo, useState } from 'react';
 import { useWizard } from '../../store/context';
+import { MD3_BTN_FILLED, MD3_BTN_OUTLINED } from '../../styles/md3-buttons';
 import {
   buildRcloneConf,
   buildIntuneInstall,
@@ -128,7 +129,7 @@ export function ReviewStep() {
         <button
           type="button"
           onClick={() => dispatch({ type: 'SET_STEP', payload: 2 })}
-          className="px-4 py-2 text-sm border border-outline rounded-md hover:bg-surface"
+          className={MD3_BTN_OUTLINED}
         >
           Back
         </button>
@@ -139,7 +140,7 @@ export function ReviewStep() {
         type="button"
         disabled={!acknowledged}
         onClick={handleDownloadZip}
-        className="w-full py-2 px-4 bg-primary text-on-primary rounded font-medium disabled:opacity-40 disabled:cursor-not-allowed hover:bg-primary"
+        className={`w-full mt-4 ${MD3_BTN_FILLED}`}
       >
         Download All (ZIP)
       </button>