update diagnostic signs configuration

Refactor the diagnostic signs setup to use a structured
table for severity levels, improving clarity and maintainability.

lua/settings.lua

@@ -52,7 +52,14 @@ vim.diagnostic.config({
       return string.format("%s: %s", diagnostic.source or "", diagnostic.message)
     end,
   },
-  signs = true,              -- Keep signs in signcolumn
+  signs = {
+    text = {
+      [vim.diagnostic.severity.ERROR] = "E",
+      [vim.diagnostic.severity.WARN] = "W",
+      [vim.diagnostic.severity.HINT] = "H",
+      [vim.diagnostic.severity.INFO] = "I",
+    },
+  },
   underline = true,          -- Underline problematic text
   update_in_insert = false,  -- Don't update diagnostics while typing
   severity_sort = true,      -- Sort by severity (errors first)
@@ -63,10 +70,3 @@ vim.diagnostic.config({
     prefix = '',
   },
 })
-
--- Diagnostic signs in signcolumn
-local signs = { Error = "E", Warn = "W", Hint = "H", Info = "I" }
-for type, icon in pairs(signs) do
-  local hl = "DiagnosticSign" .. type
-  vim.fn.sign_define(hl, { text = icon, texthl = hl, numhl = hl })
-end