feat: add connection API endpoints

Suggestions, create/confirm/hide/withdraw actions, my connections list,
and pending count for nav badge.

server/api/connections/[id]/withdraw.post.js

@@ -0,0 +1,43 @@
+import mongoose from 'mongoose'
+import Connection from '../../../models/connection.js'
+import { requireAuth } from '../../../utils/auth.js'
+
+export default defineEventHandler(async (event) => {
+  const member = await requireAuth(event)
+  const memberId = member._id
+  const connectionId = getRouterParam(event, 'id')
+
+  if (!mongoose.Types.ObjectId.isValid(connectionId)) {
+    throw createError({
+      statusCode: 400,
+      statusMessage: 'Invalid connection ID'
+    })
+  }
+
+  const connection = await Connection.findById(connectionId)
+  if (!connection) {
+    throw createError({
+      statusCode: 404,
+      statusMessage: 'Connection not found'
+    })
+  }
+
+  // Only the initiator can withdraw
+  if (connection.initiator.toString() !== memberId.toString()) {
+    throw createError({
+      statusCode: 403,
+      statusMessage: 'Only the initiator can withdraw a connection request'
+    })
+  }
+
+  if (connection.status !== 'pending') {
+    throw createError({
+      statusCode: 400,
+      statusMessage: 'Can only withdraw pending connections'
+    })
+  }
+
+  await Connection.findByIdAndDelete(connectionId)
+
+  return { success: true }
+})