refactor(backend): add status constants and update code to use them

- Create constants/statuses.js with MATCH_STATUS, SUGGESTION_STATUS
- Update routes/dashboard.js to use MATCH_STATUS
- Update routes/matches.js to use MATCH_STATUS
- Update routes/events.js to use SUGGESTION_STATUS
- Update services/matching.js to use SUGGESTION_STATUS
- Update tests to use constants

backend/src/constants/index.js

@@ -0,0 +1,6 @@
+const { MATCH_STATUS, SUGGESTION_STATUS } = require('./statuses');
+
+module.exports = {
+  MATCH_STATUS,
+  SUGGESTION_STATUS,
+};

backend/src/constants/statuses.js

@@ -0,0 +1,24 @@
+/**
+ * Match status constants
+ */
+const MATCH_STATUS = {
+  PENDING: 'pending',
+  ACCEPTED: 'accepted',
+  REJECTED: 'rejected',
+  COMPLETED: 'completed',
+};
+
+/**
+ * Suggestion status constants (for auto-matching)
+ */
+const SUGGESTION_STATUS = {
+  PENDING: 'pending',
+  ACCEPTED: 'accepted',
+  REJECTED: 'rejected',
+  NOT_FOUND: 'not_found',
+};
+
+module.exports = {
+  MATCH_STATUS,
+  SUGGESTION_STATUS,
+};