feat: add license admin API for runtime license updates

- GET /api/v1/admin/license returns current license info
- POST /api/v1/admin/license validates and loads new license token
- Requires ADMIN role, validates Ed25519 signature before applying
- OpenAPI annotations for Swagger documentation

cameleer3-server-app/src/main/java/com/cameleer3/server/app/controller/LicenseAdminController.java

@@ -0,0 +1,53 @@
+package com.cameleer3.server.app.controller;
+
+import com.cameleer3.server.core.license.LicenseGate;
+import com.cameleer3.server.core.license.LicenseInfo;
+import com.cameleer3.server.core.license.LicenseValidator;
+import io.swagger.v3.oas.annotations.Operation;
+import io.swagger.v3.oas.annotations.tags.Tag;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.http.ResponseEntity;
+import org.springframework.security.access.prepost.PreAuthorize;
+import org.springframework.web.bind.annotation.*;
+
+import java.util.Map;
+
+@RestController
+@RequestMapping("/api/v1/admin/license")
+@PreAuthorize("hasRole('ADMIN')")
+@Tag(name = "License Admin", description = "License management")
+public class LicenseAdminController {
+
+    private final LicenseGate licenseGate;
+    private final String licensePublicKey;
+
+    public LicenseAdminController(LicenseGate licenseGate,
+                                   @Value("${license.public-key:}") String licensePublicKey) {
+        this.licenseGate = licenseGate;
+        this.licensePublicKey = licensePublicKey;
+    }
+
+    @GetMapping
+    @Operation(summary = "Get current license info")
+    public ResponseEntity<LicenseInfo> getCurrent() {
+        return ResponseEntity.ok(licenseGate.getCurrent());
+    }
+
+    record UpdateLicenseRequest(String token) {}
+
+    @PostMapping
+    @Operation(summary = "Update license token at runtime")
+    public ResponseEntity<?> update(@RequestBody UpdateLicenseRequest request) {
+        if (licensePublicKey == null || licensePublicKey.isBlank()) {
+            return ResponseEntity.badRequest().body(Map.of("error", "No license public key configured"));
+        }
+        try {
+            LicenseValidator validator = new LicenseValidator(licensePublicKey);
+            LicenseInfo info = validator.validate(request.token());
+            licenseGate.load(info);
+            return ResponseEntity.ok(info);
+        } catch (Exception e) {
+            return ResponseEntity.badRequest().body(Map.of("error", e.getMessage()));
+        }
+    }
+}