fix: implement random-port discovery for CI E2E backend

When PORT=0, the backend now writes its actual bound port to
data/test/.port. test-env.sh reads that file when TT_TEST_PORT=0
so all targets (test-up, test-reset, test-down) resolve the real URL.
test-up waits for .port to appear before the health-check loop.

scripts/test-env.sh

@@ -13,6 +13,15 @@ if [ "${TT_TEST_PORT_RANDOM:-0}" = "1" ]; then
   TT_TEST_PORT=0
 fi
 
+# If port is 0 and the backend already wrote its actual port, use it
+_port_file="${TT_WORKTREE_ROOT}/data/test/.port"
+if [ "$TT_TEST_PORT" = "0" ] && [ -f "$_port_file" ]; then
+  _real_port=$(cat "$_port_file")
+  if [ -n "$_real_port" ] && [ "$_real_port" != "0" ]; then
+    TT_TEST_PORT=$_real_port
+  fi
+fi
+
 TT_TEST_DB="${TT_WORKTREE_ROOT}/data/test/attendance.db"
 TT_TEST_MODE=1
 TT_BASE_URL="http://127.0.0.1:${TT_TEST_PORT}"