feat: subcomando doctor (verificacion post-instalacion)

- core/doctor.sh: run_doctor_checks() — symlink estable, version.txt, clinfo, vainfo, grupos render/video; salida con print_*, exit code = numero de checks con fallo
- clinfo/vainfo con patron captura-then-parse (clinfo tiene salida enorme: grep -q SIGPIPE-mata la pipe y reportaba falso negativo bajo pipefail — verificado en sistema real con plataforma OpenCL detectada)
- main.sh: dispatch del subcomando ANTES del root check (el doctor es verificacion de usuario, sin root) — requiere el reorden routes/source antes de privilegios (resuelve la causa raiz de O2; el cambio cosmico echo->print_error queda para fase siguiente)

main.sh

@@ -7,13 +7,6 @@ set -euo pipefail
 # It supports Debian 13, Ubuntu 22.04/24.04/26.04, and Fedora (latest stable versions).
 # ------------------------------------------------------------------------------
 
-# privileges
-if [ "$EUID" -ne 0 ]; then
-    echo "ERROR: This script must be run as root. Use:"
-    echo "  sudo bash $0"
-    exit 1
-fi
-
 # routes
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 CORE_DIR="$SCRIPT_DIR/core"
@@ -22,6 +15,22 @@ MODULES_DIR="$SCRIPT_DIR/modules"
 # print
 source "$CORE_DIR/common.sh"
 
+# Subcommands (before the root check: doctor is a post-install user verification)
+case "${1:-}" in
+    doctor)
+        source "$CORE_DIR/doctor.sh"
+        run_doctor_checks
+        exit 0
+        ;;
+esac
+
+# privileges
+if [ "$EUID" -ne 0 ]; then
+    echo "ERROR: This script must be run as root. Use:"
+    echo "  sudo bash $0"
+    exit 1
+fi
+
 print_step "============================================="
 print_step "  OpenVINO 2026 - SimpleInstaller"
 print_step "============================================="