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

@@ -35,10 +35,6 @@ tested.
 
 # Completed Steps
 
-- 2026-10-27: README "Rationale" says why RouteWatch exists: to answer our other
-  services' questions about IP addresses, from its own routing table and the
-  WHOIS details it keeps. It still says what RIS Live does not give (closes
-  #204)
 - 2026-10-27: every JSON answer carries `@meta`. A panic on a JSON route answers
   500 with the JSON error body. `/status.json` and the health check answer 405
   with the JSON error body to any method they do not take. The 500 and the 405