refactor(repo): consolidate openflare-server to root and move subprojects to internal/apps

- Merge all files inside openflare-server to the repository root directory.
- Relocate agent, relay, and flared subprojects from internal/ to internal/apps/.
- Combine docker-compose files and update build context paths to root.
- Update GitHub workflows and Dockerfiles to refer to new directories and package names.
- Rewrite Go package imports across all files.
- Resolve database renew test race condition and clean up docs.

internal/apps/agent/updater/restart_unix_test.go

@@ -0,0 +1,15 @@
+//go:build !windows
+
+package updater
+
+import (
+	"path/filepath"
+	"testing"
+)
+
+func TestRemoveBackupBinaryIgnoresMissingFile(t *testing.T) {
+	backupPath := filepath.Join(t.TempDir(), "openflare-agent.bak")
+	if err := removeBackupBinary(backupPath); err != nil {
+		t.Fatalf("expected missing backup cleanup to be ignored: %v", err)
+	}
+}