feat: add captcha verification to contact form

Added math-based captcha system to prevent spam on the contact form:
- Created captcha API endpoint with simple arithmetic questions
- Added captcha UI component with refresh functionality
- Integrated captcha verification into contact form submission
- Relaxed spam filters since captcha provides better protection

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/api/captcha/route.ts

@@ -0,0 +1,50 @@
+import { NextResponse } from 'next/server'
+import { generateCaptcha, verifyCaptcha } from '@/lib/captcha'
+
+export const runtime = 'nodejs'
+
+export async function GET() {
+  try {
+    const captchaData = generateCaptcha()
+
+    return NextResponse.json({
+      success: true,
+      captchaId: captchaData.captchaId,
+      question: captchaData.question
+    })
+
+  } catch (error) {
+    console.error('Captcha generation error:', error)
+    return NextResponse.json({
+      success: false,
+      error: 'Failed to generate captcha'
+    }, { status: 500 })
+  }
+}
+
+export async function POST(request: Request) {
+  try {
+    const { captchaId, answer } = await request.json()
+
+    if (!captchaId || answer === undefined) {
+      return NextResponse.json({
+        success: false,
+        error: 'Missing captcha ID or answer'
+      }, { status: 400 })
+    }
+
+    const isValid = verifyCaptcha(captchaId, answer)
+
+    return NextResponse.json({
+      success: true,
+      valid: isValid
+    })
+
+  } catch (error) {
+    console.error('Captcha verification error:', error)
+    return NextResponse.json({
+      success: false,
+      error: 'Failed to verify captcha'
+    }, { status: 500 })
+  }
+}