Phase 0: remove auto-updater, pin Go 1.27.1, fix vet warnings, tidy ignores

- Delete BinaryUpdate, internal/up2date, GitHub/Update structs and the
  xteveAutoUpdate / update.url settings (UI rows, en.json, defaults).
  Settings-schema migrations kept and moved to src/migrate.go.
- Drop kardianos/osext dependency.
- xteve.go version 0200 -> 0201 to match changelog; Drone now fails on drift.
- go.mod go 1.27.1; Dockerfile and Drone golang images pinned to 1.27.1.
- Fix four go vet unreachable-code warnings.
- .gitignore: .gocache/, agent.md, skill.md. .dockerignore: build context
  no longer includes caches, ts/, tasks/ or markdown except the changelog.
- Drone: publish :latest only from master; other branches publish a
  branch-named tag so a feature push cannot replace the deployed image.
- Add tasks/improvement-plan.md and tasks/todo.md.
- Regenerate src/webUI.go.

src/migrate.go

@@ -0,0 +1,156 @@
+package src
+
+import (
+	"errors"
+	"fmt"
+	"reflect"
+)
+
+// conditionalUpdateChanges : Settings-schema migrations applied at start-up.
+// (Binary self-update was removed; the Docker image is the only distribution channel.)
+func conditionalUpdateChanges() (err error) {
+
+checkVersion:
+	settingsMap, err := loadJSONFileToMap(System.File.Settings)
+	if err != nil || len(settingsMap) == 0 {
+		return
+	}
+
+	if settingsVersion, ok := settingsMap["version"].(string); ok {
+
+		if settingsVersion > System.DBVersion {
+			showInfo("Settings DB Version:" + settingsVersion)
+			showInfo("System DB Version:" + System.DBVersion)
+			err = errors.New(getErrMsg(1031))
+			return
+		}
+
+		// Letzte Kompatible Version (1.4.4)
+		if settingsVersion < System.Compatibility {
+			err = errors.New(getErrMsg(1013))
+			return
+		}
+
+		switch settingsVersion {
+
+		case "1.4.4":
+			// UUID Wert in xepg.json setzen
+			err = setValueForUUID()
+			if err != nil {
+				return
+			}
+
+			// Neuer Filter (WebUI). Alte Filtereinstellungen werden konvertiert
+			if oldFilter, ok := settingsMap["filter"].([]any); ok {
+				var newFilterMap = convertToNewFilter(oldFilter)
+				settingsMap["filter"] = newFilterMap
+
+				settingsMap["version"] = "2.0.0"
+
+				err = saveMapToJSONFile(System.File.Settings, settingsMap)
+				if err != nil {
+					return
+				}
+
+				goto checkVersion
+
+			} else {
+				err = errors.New(getErrMsg(1030))
+				return
+			}
+
+		case "2.0.0":
+
+			if oldBuffer, ok := settingsMap["buffer"].(bool); ok {
+
+				var newBuffer string
+				switch oldBuffer {
+				case true:
+					newBuffer = "xteve"
+				case false:
+					newBuffer = "-"
+				}
+
+				settingsMap["buffer"] = newBuffer
+
+				settingsMap["version"] = "2.1.0"
+
+				err = saveMapToJSONFile(System.File.Settings, settingsMap)
+				if err != nil {
+					return
+				}
+
+				goto checkVersion
+
+			} else {
+				err = errors.New(getErrMsg(1030))
+				return
+			}
+
+		case "2.1.0":
+			// Falls es in einem späteren Update Änderungen an der Datenbank gibt, geht es hier weiter
+
+			break
+		}
+
+	} else {
+		// settings.json ist zu alt (älter als Version 1.4.4)
+		err = errors.New(getErrMsg(1013))
+	}
+
+	return
+}
+
+func convertToNewFilter(oldFilter []any) (newFilterMap map[int]any) {
+
+	newFilterMap = make(map[int]any)
+
+	switch reflect.TypeFor[[]any]().Kind() {
+
+	case reflect.Slice:
+		s := reflect.ValueOf(oldFilter)
+
+		for i := 0; i < s.Len(); i++ {
+
+			var newFilter FilterStruct
+			newFilter.Active = true
+			newFilter.Name = fmt.Sprintf("Custom filter %d", i+1)
+			newFilter.Filter = s.Index(i).Interface().(string)
+			newFilter.Type = "custom-filter"
+			newFilter.CaseSensitive = false
+
+			newFilterMap[i] = newFilter
+
+		}
+
+	}
+
+	return
+}
+
+func setValueForUUID() (err error) {
+
+	xepg, err := loadJSONFileToMap(System.File.XEPG)
+
+	for _, c := range xepg {
+
+		var xepgChannel = c.(map[string]any)
+
+		if uuidKey, ok := xepgChannel["_uuid.key"].(string); ok {
+
+			if value, ok := xepgChannel[uuidKey].(string); ok {
+
+				if len(value) > 0 {
+					xepgChannel["_uuid.value"] = value
+				}
+
+			}
+
+		}
+
+	}
+
+	err = saveMapToJSONFile(System.File.XEPG, xepg)
+
+	return
+}