Drop leftover reasoning from the old dev default

The README Docker and nginx examples no longer set
WEBHOOKER_ENVIRONMENT=prod, which is now the default. The
TRUSTED_PROXIES warning text in the README, config.go and its test now
gives the real reason it ignores the environment: behind a proxy every
client shares one bucket in dev and prod alike.

Model: opus-5-5

README.md

@@ -400,10 +400,9 @@ the bucket is. See [Rate Limiting](#rate-limiting).
 
 The remedy is to set `TRUSTED_PROXIES` to your reverse proxy's
 address, which restores per-client buckets. webhooker logs a warning
-at startup whenever `TRUSTED_PROXIES` is empty, in every environment —
-the warning does not depend on `WEBHOOKER_ENVIRONMENT`, because an
-operator who never configured the deployment is precisely the one at
-risk. The warning is informational when nothing proxies to the
+at startup whenever `TRUSTED_PROXIES` is empty, in every environment,
+because behind a proxy every client shares one bucket in `dev` and
+`prod` alike. The warning is informational when nothing proxies to the
 process: with no proxy in front, the peer address is the client's own
 and the buckets are already per-client. See
 [Rate Limiting](#rate-limiting) for what each limit shares.
@@ -639,7 +638,6 @@ decision:
 docker run -d \
   -p 127.0.0.1:8080:8080 \
   -v /path/to/data:/var/lib/webhooker \
-  -e WEBHOOKER_ENVIRONMENT=prod \
   -e BIND_ADDRESS=0.0.0.0 \
   webhooker:latest
 ```
@@ -856,7 +854,6 @@ sent — `$scheme` above does.
 With that block, webhooker's environment is:
 
 ```sh
-WEBHOOKER_ENVIRONMENT=prod
 BIND_ADDRESS=127.0.0.1   # the default; stated here to be explicit
 TRUSTED_PROXIES=127.0.0.1
 ```