feat(core): add any() route registration, warn on undocumented OpenAPI routes, log unhandled 500s

FlashRegistrar#any() registers a handler under every HTTP method for
verb-indifferent handlers (e.g. a reverse proxy). OpenApiExtension now warns
when a class-based handler has no @ApiOperation instead of silently omitting
it from the spec. AbstractRouter's default production exception handler now
logs unhandled exceptions server-side instead of only returning a JSON 500.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

flash/src/main/java/dev/relism/flash/extension/FlashRegistrar.java

@@ -51,6 +51,12 @@ public abstract class FlashRegistrar<SELF extends FlashRegistrar<SELF>> {
     public final SELF purge  (String path, SimpleHandler.FunctionalHandler h, Middleware... mw) { return route(HttpMethod.PURGE,   path, h, mw); }
     public final SELF query  (String path, SimpleHandler.FunctionalHandler h, Middleware... mw) { return route(HttpMethod.QUERY,   path, h, mw); }
 
+    /** Registers {@code h} under every {@link HttpMethod}: for handlers indifferent to verb (e.g. a proxy). */
+    public final SELF any(String path, SimpleHandler.FunctionalHandler h, Middleware... mw) {
+        for (HttpMethod m : HttpMethod.values()) route(m, path, h, mw);
+        return (SELF) this;
+    }
+
     public final SELF getWith    (String path, SimpleHandler.FunctionalHandler h, MiddlewareNode... mw) { return route(HttpMethod.GET,     path, h, mw); }
     public final SELF postWith   (String path, SimpleHandler.FunctionalHandler h, MiddlewareNode... mw) { return route(HttpMethod.POST,    path, h, mw); }
     public final SELF putWith    (String path, SimpleHandler.FunctionalHandler h, MiddlewareNode... mw) { return route(HttpMethod.PUT,     path, h, mw); }

flash/src/main/java/dev/relism/flash/routing/AbstractRouter.java

@@ -7,6 +7,7 @@ import dev.relism.flash.Flash;
 import dev.relism.flash.http.ContentType;
 import dev.relism.flash.http.HttpMethod;
 import dev.relism.flash.template.ErrorPages;
+import lombok.extern.slf4j.Slf4j;
 
 import java.nio.charset.StandardCharsets;
 
@@ -29,6 +30,7 @@ import java.nio.charset.StandardCharsets;
  * <p><b>Registration</b>: use {@link FlashApp} — the single
  * public registration API. {@link #doRegister} is an infrastructure method.
  */
+@Slf4j
 public abstract class AbstractRouter {
 
     /** Eagerly validates and compiles this route graph before traffic is accepted. */
@@ -59,6 +61,7 @@ public abstract class AbstractRouter {
                 return ErrorPages.renderException(req, ex);
             }
             : (ex, req, res) -> {
+                log.error("Unhandled exception in {} {}", req.method(), req.path(), ex);
                 res.status(500);
                 res.type(ContentType.JSON);
                 return JSON_500;