fix(installer): rename .env.example -> env.example, WAF blocks .env* paths

Found live during a real install dry-run: fetching .env.example via the
Gitea raw URL returned a 403 with an ARGUS-branded WAF block page --
Weboria's own front-line WAF blocks any request path matching .env* as a
standard credential-harvesting-probe rule, and it caught this legitimate
static file served from Gitea too. Confirmed docker-compose.yml and other
non-.env-named files fetch fine; only the .env.example path was affected.

Renamed to env.example (no leading dot) rather than requesting a WAF
exception -- sidesteps the false positive without depending on
infrastructure access this session doesn't have. Still saved locally as
.env either way; only the remote filename changed.

install.sh

@@ -54,8 +54,13 @@ for script in update.sh uninstall.sh healthcheck.sh backup.sh restore.sh; do
   fetch "$script" "$script"
   chmod +x "$script"
 done
+# The repo stores this as env.example (no leading dot) rather than .env.example
+# -- Weboria's own WAF blocks any request path matching .env* as a standard
+# credential-harvesting-probe rule, which also caught this legitimate static
+# file when served from Gitea. Renaming sidesteps it without needing a WAF
+# exception. Saved locally as .env either way.
 if [ ! -f .env ]; then
-  fetch ".env.example" ".env"
+  fetch "env.example" ".env"
   ok "Fetched deployment files into $INSTALL_DIR"
 else
   ok "Fetched compose file (kept your existing .env)"