Refuse invalid settings at start, health check follows PORT (closes #31)

A set but invalid PORT (anything but plain digits from 1 to 65535) or a relative XDG_DATA_HOME now stops the start before the database opens; before, a bad PORT left the daemon running without HTTP. entrypoint.sh refuses a MALLOC_ARENA_MAX that is not a positive whole number, since glibc ignores a bad one silently. The HEALTHCHECK probes the port PORT names, 8080 when unset. PORT is now read in internal/config, so server.New takes the config.

The README gives the real Linux state directory, lists XDG_DATA_HOME, and adds "Running under upaas": port, volume, environment, the 5g memory limit and the health check.

Unverified: the 5g memory limit could not be exercised on the build host.

Model: opus-5-5

internal/routewatch/app_integration_test.go

@@ -450,7 +450,7 @@ func TestRouteWatchLiveFeed(t *testing.T) {
 	}
 
 	// Create server
-	srv := server.New(mockDB, s, logger)
+	srv := server.New(mockDB, s, logger, cfg)
 
 	// Create RouteWatch with 5 second limit
 	deps := Dependencies{