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/server/handlers_test.go

@@ -8,6 +8,7 @@ import (
 	"testing"
 	"time"
 
+	"git.eeqj.de/sneak/routewatch/internal/config"
 	"git.eeqj.de/sneak/routewatch/internal/database"
 	"git.eeqj.de/sneak/routewatch/internal/logger"
 	"git.eeqj.de/sneak/routewatch/internal/metrics"
@@ -38,7 +39,7 @@ func (d blockingStatsDB) GetStatsContext(_ context.Context) (database.Stats, err
 func TestStatsHandlersDoNotLeakOnTimeout(t *testing.T) {
 	release := make(chan struct{})
 	db := blockingStatsDB{release: release}
-	s := New(db, streamer.New(logger.New(), metrics.New()), logger.New())
+	s := New(db, streamer.New(logger.New(), metrics.New()), logger.New(), &config.Config{})
 
 	handlers := map[string]http.HandlerFunc{
 		"status.json": s.handleStatusJSON(),