add session-based connection management and React dashboard

Backend: adds JDBC session support, login/status/logout endpoints, and
new DTOs (AuthResponse, ConnectionStatusResponse, LoginResult). Frontend
replaces the Vite boilerplate with a Dashboard, ServiceCard, and
ConnectModal backed by a typed API client.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main/java/com/vaessl/app/connection/ConnectionController.java

@@ -1,13 +1,26 @@
 package com.vaessl.app.connection;
 
+import java.time.Instant;
+import java.time.temporal.ChronoUnit;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
 import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.DeleteMapping;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PathVariable;
 import org.springframework.web.bind.annotation.PostMapping;
 import org.springframework.web.bind.annotation.RequestBody;
 import org.springframework.web.bind.annotation.RestController;
 
+import com.vaessl.app.dto.AuthResponse;
 import com.vaessl.app.dto.ConnectionRequest;
-import com.vaessl.app.dto.ConnectionResponse;
+import com.vaessl.app.dto.ConnectionStatusResponse;
+import com.vaessl.app.dto.LoginResult;
 
+import jakarta.servlet.http.HttpServletRequest;
+import jakarta.servlet.http.HttpSession;
 import jakarta.validation.Valid;
 import lombok.RequiredArgsConstructor;
 
@@ -15,10 +28,63 @@ import lombok.RequiredArgsConstructor;
 @RequiredArgsConstructor
 public class ConnectionController {
 
+    private static final String SUFFIX = "_CONNECTION_ID";
+
     private final ConnectionService connectionService;
 
     @PostMapping("/login")
-    public ResponseEntity<ConnectionResponse> loginResponse(@Valid @RequestBody ConnectionRequest request) {
-        return ResponseEntity.ok(connectionService.login(request));
+    public ResponseEntity<AuthResponse> login(
+            @Valid @RequestBody ConnectionRequest request,
+            HttpServletRequest httpReq) {
+
+        LoginResult result = connectionService.login(request);
+
+        HttpSession session = httpReq.getSession(true);
+        session.setAttribute(request.serviceType() + SUFFIX, result.connectionId());
+
+        if (result.expiresAt() != null) {
+            long secs = Instant.now().until(result.expiresAt(), ChronoUnit.SECONDS);
+            session.setMaxInactiveInterval((int) Math.max(secs, 300));
+        }
+
+        return ResponseEntity.ok(new AuthResponse(request.serviceType(), result.expiresAt()));
+    }
+
+    @GetMapping("/connections/status")
+    public ResponseEntity<List<ConnectionStatusResponse>> getStatus(HttpServletRequest httpReq) {
+        HttpSession session = httpReq.getSession(false);
+        if (session == null) {
+            return ResponseEntity.ok(List.of());
+        }
+
+        List<ConnectionStatusResponse> statuses = new ArrayList<>();
+        Collections.list(session.getAttributeNames()).stream()
+                .filter(k -> k.endsWith(SUFFIX))
+                .forEach(k -> {
+                    String serviceType = k.replace(SUFFIX, "");
+                    Long id = (Long) session.getAttribute(k);
+                    ConnectionStatusResponse status = connectionService.getConnectionStatus(serviceType, id);
+                    if (status != null) statuses.add(status);
+                });
+
+        return ResponseEntity.ok(statuses);
+    }
+
+    @DeleteMapping("/connections/{serviceType}")
+    public ResponseEntity<Void> logout(
+            @PathVariable("serviceType") String serviceType,
+            HttpServletRequest httpReq) {
+
+        HttpSession session = httpReq.getSession(false);
+        if (session != null) {
+            session.removeAttribute(serviceType + SUFFIX);
+            boolean hasMore = Collections.list(session.getAttributeNames()).stream()
+                    .anyMatch(k -> k.endsWith(SUFFIX));
+            if (!hasMore) {
+                session.invalidate();
+            }
+        }
+
+        return ResponseEntity.noContent().build();
     }
 }