Stop describing dev as the default environment

Comments in reqtls and session, and the README Quick Start and
deployment checklist, still spoke as if an unset WEBHOOKER_ENVIRONMENT
meant dev. The checklist now asks only that the environment is not dev
(unset or prod); the Quick Start describes running from the clone.

Model: opus-5-5

README.md

@@ -44,9 +44,9 @@ make bootstrap
 # Run all checks (test, lint, format check)
 make check
 
-# Run in development mode. DATA_DIR defaults to /var/lib/webhooker in
-# every environment, so set it (in .env or the shell) to a writable
-# directory when running from a clone.
+# Run the server from the clone. DATA_DIR defaults to
+# /var/lib/webhooker in every environment, so set it (in .env or the
+# shell) to a writable directory.
 DATA_DIR=./data make dev
 
 # Build Docker image
@@ -753,17 +753,18 @@ reports.
    serves the admin login form and the unauthenticated receiver with
    no TLS at all, and the proxy in front of it changes nothing about
    that.
-2. **Set `WEBHOOKER_ENVIRONMENT=prod`, and make sure the proxy sends
-   `X-Forwarded-Proto`.** These are two requirements, not one. The
-   environment setting decides CORS and nothing else: `dev` answers
-   every origin with `Access-Control-Allow-Origin: *` (without
-   credentials), which a server-rendered production deployment has no
-   use for, and `prod` — the default — disables it. Cookie `Secure`
-   and the strict Origin/Referer mode are **not** tied to it — they
-   are decided per request from the transport, which behind a proxy
-   means the `X-Forwarded-Proto` header. The block below sets it;
-   without it every request is read as plaintext and cookies ship
-   without `Secure`. See [Configuration](#configuration).
+2. **Make sure the environment is not `dev` (leave
+   `WEBHOOKER_ENVIRONMENT` unset or set it to `prod`), and make sure
+   the proxy sends `X-Forwarded-Proto`.** These are two requirements,
+   not one. The environment setting decides CORS and nothing else:
+   `dev` answers every origin with `Access-Control-Allow-Origin: *`
+   (without credentials), which a server-rendered production
+   deployment has no use for, and `prod` — the default — disables it.
+   Cookie `Secure` and the strict Origin/Referer mode are **not** tied
+   to it — they are decided per request from the transport, which
+   behind a proxy means the `X-Forwarded-Proto` header. The block below
+   sets it; without it every request is read as plaintext and cookies
+   ship without `Secure`. See [Configuration](#configuration).
 3. **Set `TRUSTED_PROXIES` to the proxy's address.** Unset, every rate
    limiter keys on the connecting peer, which behind a proxy is the
    proxy on every request: all clients collapse into one global bucket