feat: add auto_update config, clarify auto_install vs auto_update vs auto_check

- auto_install (default: true) — install missing binaries on register
- auto_check (default: true) — check for available updates periodically
- auto_update (default: false) — auto-update when newer versions found
- Disabling auto_check also disables auto_update
- Updated README and help docs

README.md

@@ -133,9 +133,12 @@ require("glaze").setup({
     silent = false,      -- Suppress install notifications
   },
   auto_check = {
-    enabled = true,      -- Auto-check for updates
+    enabled = true,      -- Auto-check for updates (disabling also disables auto_update)
     frequency = "daily", -- "daily", "weekly", or hours as number
   },
+  auto_update = {
+    enabled = false,     -- Auto-update binaries when newer versions are found (requires auto_check)
+  },
 })
 ```