feat: implement Ratings API (Phase 2.5)

Complete the match lifecycle with partner rating functionality.

Backend changes:
- Add POST /api/matches/:slug/ratings endpoint to create ratings
  * Validate score range (1-5)
  * Prevent duplicate ratings (unique constraint per match+rater+rated)
  * Auto-complete match when both users have rated
  * Return detailed rating data with user and event info
- Add GET /api/users/:username/ratings endpoint to fetch user ratings
  * Calculate and return average rating
  * Include rater details and event context for each rating
  * Limit to last 50 ratings
- Add hasRated field to GET /api/matches/:slug response
  * Check if current user has already rated the match
  * Enable frontend to prevent duplicate rating attempts

Frontend changes:
- Update RatePartnerPage to use real API instead of mocks
  * Load match data and partner info
  * Submit ratings with score, comment, and wouldCollaborateAgain
  * Check hasRated flag and redirect if already rated
  * Validate match status before allowing rating
  * Show loading state and proper error handling
- Update MatchChatPage to show rating status
  * Replace "Rate Partner" button with "✓ Rated" badge when user has rated
  * Improve button text from "End & rate" to "Rate Partner"
- Add ratings API functions
  * matchesAPI.createRating(slug, ratingData)
  * ratingsAPI.getUserRatings(username)

User flow:
1. After match is accepted, users can rate each other
2. Click "Rate Partner" in chat to navigate to rating page
3. Submit 1-5 star rating with optional comment
4. Rating saved and user redirected to matches list
5. Chat shows "✓ Rated" badge instead of rating button
6. Match marked as 'completed' when both users have rated
7. Users cannot rate the same match twice

frontend/src/pages/RatePartnerPage.jsx

@@ -1,20 +1,53 @@
-import { useState } from 'react';
+import { useState, useEffect } from 'react';
 import { useParams, useNavigate } from 'react-router-dom';
 import Layout from '../components/layout/Layout';
-import { mockUsers } from '../mocks/users';
-import { Star } from 'lucide-react';
+import { matchesAPI } from '../services/api';
+import { Star, Loader2 } from 'lucide-react';
 
 const RatePartnerPage = () => {
   const { slug } = useParams();
   const navigate = useNavigate();
+  const [match, setMatch] = useState(null);
+  const [loading, setLoading] = useState(true);
   const [rating, setRating] = useState(0);
   const [hoveredRating, setHoveredRating] = useState(0);
   const [comment, setComment] = useState('');
   const [wouldCollaborateAgain, setWouldCollaborateAgain] = useState(true);
   const [submitting, setSubmitting] = useState(false);
 
-  // Partner user (mockup)
-  const partner = mockUsers[1]; // sarah_swing
+  // Load match data and check if already rated
+  useEffect(() => {
+    const loadMatch = async () => {
+      try {
+        setLoading(true);
+        const result = await matchesAPI.getMatch(slug);
+        setMatch(result.data);
+
+        // Check if this match can be rated
+        if (result.data.status !== 'accepted' && result.data.status !== 'completed') {
+          alert('This match must be accepted before rating.');
+          navigate('/matches');
+          return;
+        }
+
+        // Check if user has already rated this match
+        if (result.data.hasRated) {
+          alert('You have already rated this match.');
+          navigate('/matches');
+          return;
+        }
+      } catch (error) {
+        console.error('Failed to load match:', error);
+        alert('Failed to load match. Redirecting to matches page.');
+        navigate('/matches');
+      } finally {
+        setLoading(false);
+      }
+    };
+    loadMatch();
+  }, [slug, navigate]);
+
+  const partner = match?.partner;
 
   const handleSubmit = async (e) => {
     e.preventDefault();
@@ -25,13 +58,37 @@ const RatePartnerPage = () => {
 
     setSubmitting(true);
 
-    // Mockup - in the future will be API call
-    setTimeout(() => {
-      alert('Rating saved!');
-      navigate('/history');
-    }, 500);
+    try {
+      await matchesAPI.createRating(slug, {
+        score: rating,
+        comment: comment.trim() || null,
+        wouldCollaborateAgain,
+      });
+
+      alert('Rating submitted successfully!');
+      navigate('/matches');
+    } catch (error) {
+      console.error('Failed to submit rating:', error);
+      if (error.message?.includes('already rated')) {
+        alert('You have already rated this match.');
+      } else {
+        alert('Failed to submit rating. Please try again.');
+      }
+    } finally {
+      setSubmitting(false);
+    }
   };
 
+  if (loading || !match || !partner) {
+    return (
+      <Layout>
+        <div className="flex justify-center items-center py-12">
+          <Loader2 className="w-8 h-8 animate-spin text-primary-600" />
+        </div>
+      </Layout>
+    );
+  }
+
   return (
     <Layout>
       <div className="max-w-2xl mx-auto">
@@ -43,13 +100,17 @@ const RatePartnerPage = () => {
           {/* Partner Info */}
           <div className="flex items-center justify-center space-x-4 mb-8 p-6 bg-gray-50 rounded-lg">
             <img
-              src={partner.avatar}
+              src={partner.avatar || `https://api.dicebear.com/7.x/avataaars/svg?seed=${partner.username}`}
               alt={partner.username}
               className="w-16 h-16 rounded-full"
             />
             <div>
-              <h3 className="text-xl font-bold text-gray-900">{partner.username}</h3>
-              <p className="text-gray-600">⭐ {partner.rating} • {partner.matches_count} collaborations</p>
+              <h3 className="text-xl font-bold text-gray-900">
+                {partner.firstName && partner.lastName
+                  ? `${partner.firstName} ${partner.lastName}`
+                  : partner.username}
+              </h3>
+              <p className="text-gray-600">@{partner.username}</p>
             </div>
           </div>