Give every JSON answer @meta, errors included (closes #201)

A panic in a JSON route's handler answered 500 with an empty body,
because the router's recoverer sits outside the middleware that adds
`@meta`. `JSONValidationMiddleware` now wraps the handler in the same
recoverer, and answers the panic with the JSON error body.

A method that `/status.json` or the health check does not take got
chi's empty 405. Each such method now goes to the JSON 405 that the
routes under `/api/v1` and `/ip` give.

The home page's IP lookup card showed only the answer's `data`. It now
shows the whole answer, `@meta` included.

A table test checks `@meta` on every JSON route, in its successes and
its errors.

Model: opus-5-5

internal/templates/index.html

@@ -714,7 +714,8 @@
                 });
         });
 
-        // IP lookup
+        // IP lookup: show the whole JSON answer, its @meta and an error answer
+        // included, as the IP information API card does.
         document.getElementById('ip-form').addEventListener('submit', function(e) {
             e.preventDefault();
             const ip = document.getElementById('ip-input').value.trim();
@@ -730,18 +731,11 @@
 
             fetch('/ip/' + encodeURIComponent(ip))
                 .then(response => response.json())
-                .then(response => {
-                    contentEl.classList.remove('loading');
-                    if (response.status === 'error') {
-                        contentEl.className = 'error';
-                        contentEl.textContent = 'Error: ' + response.error.msg;
-                    } else {
-                        contentEl.className = '';
-                        contentEl.textContent = JSON.stringify(response.data, null, 2);
-                    }
+                .then(answer => {
+                    contentEl.className = '';
+                    contentEl.textContent = JSON.stringify(answer, null, 2);
                 })
                 .catch(error => {
-                    contentEl.classList.remove('loading');
                     contentEl.className = 'error';
                     contentEl.textContent = 'Error: ' + error.message;
                 });