Set the server's public URL from KEEPORG_EXTERNAL_URL

The image passes neither -config nor -url, so a deployment had no way to
set external_url and the server built invite links, device-approval pages
and the OIDC redirect URI on http://localhost:8765. The variable overrides
the configuration file and -url overrides it. The deployment values set it
to https://keeporg.tiredsysadmin.cc.

Also document every environment variable the server reads, and the
standard proxy and CA variables it honours for OIDC.

Server version 0.8.0.

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

versions.mk

@@ -1,6 +1,6 @@
 # Single source of truth for all platform versions (semver).
 # Bump with: make bump PLATFORM=<server|linux|macos|windows|bsd|android> PART=<major|minor|patch>
-VERSION_SERVER   := 0.7.0
+VERSION_SERVER   := 0.8.0
 VERSION_LINUX    := 0.5.0
 VERSION_MACOS    := 0.5.0
 VERSION_WINDOWS  := 0.5.0