feat: add controller self-update mechanism (v0.16.0)

New selfupdate package: version parsing, audit state file, updater with
Gitea registry V2 check, docker pull + compose rewrite + compose up flow.

- API: /api/selfupdate/{status,check,update} with session+bearer auth
- UI: Settings "Verzió és frissítés" card with check/install buttons + JS polling
- Scheduler: periodic check (6h default) + optional daily auto-update
- Notifications: success/failure on post-update startup verification
- Alert: info banner when update available
- docker-compose.yml: add directory bind mount for compose file access

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

controller/internal/selfupdate/version.go

@@ -0,0 +1,68 @@
+package selfupdate
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+// Version represents a semantic version (Major.Minor.Patch).
+type Version struct {
+	Major int
+	Minor int
+	Patch int
+	Raw   string
+}
+
+// ParseVersion parses "X.Y.Z" or "vX.Y.Z". Returns error for "dev", "latest", or invalid formats.
+func ParseVersion(s string) (Version, error) {
+	s = strings.TrimPrefix(s, "v")
+	if s == "dev" || s == "latest" || s == "" {
+		return Version{}, fmt.Errorf("invalid version: %q", s)
+	}
+	parts := strings.SplitN(s, ".", 3)
+	if len(parts) != 3 {
+		return Version{}, fmt.Errorf("invalid version format: %q (expected X.Y.Z)", s)
+	}
+	major, err := strconv.Atoi(parts[0])
+	if err != nil {
+		return Version{}, fmt.Errorf("invalid major version: %w", err)
+	}
+	minor, err := strconv.Atoi(parts[1])
+	if err != nil {
+		return Version{}, fmt.Errorf("invalid minor version: %w", err)
+	}
+	patch, err := strconv.Atoi(parts[2])
+	if err != nil {
+		return Version{}, fmt.Errorf("invalid patch version: %w", err)
+	}
+	return Version{Major: major, Minor: minor, Patch: patch, Raw: s}, nil
+}
+
+// Compare returns -1 if a < b, 0 if a == b, 1 if a > b.
+func (a Version) Compare(b Version) int {
+	if a.Major != b.Major {
+		if a.Major < b.Major {
+			return -1
+		}
+		return 1
+	}
+	if a.Minor != b.Minor {
+		if a.Minor < b.Minor {
+			return -1
+		}
+		return 1
+	}
+	if a.Patch != b.Patch {
+		if a.Patch < b.Patch {
+			return -1
+		}
+		return 1
+	}
+	return 0
+}
+
+// String returns the version as "X.Y.Z".
+func (v Version) String() string {
+	return fmt.Sprintf("%d.%d.%d", v.Major, v.Minor, v.Patch)
+}