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.

`/status.json` and the health check answered chi's empty 405 to any
method they do not take. They now answer with the same JSON 405 as the
routes under `/api/v1` and `/ip`.

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

TODO.md

@@ -36,12 +36,12 @@ tested.
 # Completed Steps
 
 - 2026-10-27: every JSON answer carries `@meta`. A panic on a JSON route answers
-  500 with the JSON error body. A method that `/status.json` or the health check
+  500 with the JSON error body. `/status.json` and the health check answer 405
-  does not take answers 405 with it, as under `/api/v1`. Both used to answer
+  with the JSON error body to any method they do not take. The 500 and the 405
-  with an empty body. The home page's IP lookup shows the whole JSON answer,
+  used to have an empty body. The home page's IP lookup shows the whole JSON
-  `@meta` included. It used to show only the answer's `data`, or only the
+  answer, `@meta` included. It used to show only the answer's `data`, or only
-  message of an error answer. A test checks `@meta` on every JSON route, in its
+  the message of an error answer. A test checks `@meta` on every JSON route, in
-  successes and its errors (closes #201)
+  its successes and its errors (closes #201)
 - 2026-10-27: every value in a JSON answer that has a unit is a number, with the
   unit at the end of its field name. `@meta.execution_time` is now
   `execution_time_ms`. The stats' `uptime`, `connection_duration` and