fix(site-finder): align VelocityBlock TS types with backend response shape

Per #147 bot review — cross-stack contract mismatch:

Backend velocity.py (PR #146 merged) returns:
  obj_id, name, dev_name, obj_class, district_name, distance_m, total_sqm_period

Frontend types had:
  obj_id, name, class, distance_m, total_sqm

Result: c.class undefined → never showed class chip; c.total_sqm undefined →
Math.round(NaN) = NaN, 'не число' в table column для всех 5 строк.

## Fix

- VelocityCompetitor.class → obj_class
- VelocityCompetitor.total_sqm → total_sqm_period
- Added optional dev_name, district_name fields
- Updated VelocityBlock.tsx — все 3 references (guard, chip render, table cell)

Refs: #34, #147

frontend/src/components/site-finder/VelocityBlock.tsx

@@ -177,7 +177,7 @@ export function VelocityBlock({ velocity }: VelocityBlockProps) {
                 >
                   <td style={{ padding: "4px 8px" }}>
                     {c.name ?? `obj#${c.obj_id}`}
-                    {c.class && (
+                    {c.obj_class && (
                       <span
                         style={{
                           marginLeft: 6,
@@ -185,7 +185,7 @@ export function VelocityBlock({ velocity }: VelocityBlockProps) {
                           color: "#9ca3af",
                         }}
                       >
-                        {c.class}
+                        {c.obj_class}
                       </span>
                     )}
                   </td>
@@ -205,7 +205,7 @@ export function VelocityBlock({ velocity }: VelocityBlockProps) {
                       fontWeight: 500,
                     }}
                   >
-                    {Math.round(c.total_sqm).toLocaleString("ru")}
+                    {Math.round(c.total_sqm_period).toLocaleString("ru")}
                   </td>
                 </tr>
               ))}

frontend/src/types/site-finder.ts

@@ -208,9 +208,11 @@ export interface Pipeline24mo {
 export interface VelocityCompetitor {
   obj_id: number;
   name: string | null;
-  class: string | null;
+  obj_class: string | null;
   distance_m: number;
-  total_sqm: number;
+  total_sqm_period: number;
+  dev_name?: string | null;
+  district_name?: string | null;
 }
 
 export interface VelocityPeriod {