Log as JSON when IPX_LOG_FORMAT=json (#91)

The log was text, so the Grafana dashboard picked lines apart with
regular expressions, and a change of wording would have blanked its
panels. With IPX_LOG_FORMAT=json each line is one JSON object: the
access log carries method, path, route, status and ms as fields (the
route passed from the routing layer in the response's extensions), and
each wire event its ev, feed, new, downloaded, failed, bytes, msg and
the rest (log_wire), beside the old message. The two startup lines that
were println! are logged, so no line breaks the JSON. Text stays the
default, for a terminal. The dashboard reads the fields with Loki's json
parser, and groups requests by route rather than path.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -170,9 +170,10 @@ Non-trivial logic leaves one runnable check behind. Pure functions (`merge_polic
   watch the shutdown channel itself; the daemon ignored SIGTERM for exactly this reason.
 * Only one daemon per socket. Removing the socket file defeats the guard and you get two daemons
   fighting over the database, with the stale one still holding the port.
-* **The Grafana dashboard parses the log** (`grafana/dashboard.py`): the access log's
-  `GET /path -> 200 in 3ms` and the events' `ipx::io: <- {json}`. Change either and the panels go
-  blank without an error; regenerate the dashboard with the new pattern.
+* **The Grafana dashboard reads the log's fields** (`grafana/dashboard.py`). Production logs JSON
+  (`IPX_LOG_FORMAT=json`); the access log's `method`, `path`, `route`, `status`, `ms` and the
+  events' `ev`, `feed`, `new`, `bytes`, `msg` (`log_wire` in ipc.rs) are what the panels query.
+  Rename one and its panels go blank without an error; regenerate the dashboard to match.
 * `/api/settings` answering `200` does **not** mean the daemon is well — the web server is a
   different task. `ipx status` checks the control socket and the database; to see the worker
   getting through its jobs, watch for `scan complete` in the log.