Add LSP diagnostic backgrounds for better visibility

Introduce light tinted backgrounds for LSP diagnostics
to enhance code highlighting and improve user experience.

lua/paper-tonic-modern/colors.lua

@@ -95,6 +95,12 @@ M.diag_warn = {'#ff6600', 202, 'red'}         -- Fluorescent orange (warnings)
 M.diag_info = {'#00ccff', 45, 'cyan'}         -- Bright fluorescent cyan (info - more prominent)
 M.diag_hint = {'#66e0ff', 81, 'cyan'}         -- Softer fluorescent cyan (hint - less prominent)
 
+-- LSP Diagnostic backgrounds - Light tinted versions for highlighting code
+M.bg_diag_error = {'#ffe6f0', 224, 'white'}   -- Very light pink (for error backgrounds)
+M.bg_diag_warn = {'#fff0e6', 223, 'white'}    -- Very light orange (for warning backgrounds)
+M.bg_diag_info = {'#e6f9ff', 195, 'white'}    -- Very light cyan (for info backgrounds)
+M.bg_diag_hint = {'#f0fcff', 195, 'white'}    -- Very light cyan (for hint backgrounds)
+
 -- ============================================================================
 -- Primary Accent Colors (brownish-red tones)
 -- ============================================================================

lua/paper-tonic-modern/groups/lsp.lua

@@ -8,30 +8,30 @@ return {
   -- LSP Diagnostics
   -- ============================================================================
   
-  -- Error diagnostics (fluorescent hot pink)
+  -- Error diagnostics (fluorescent hot pink with light pink background)
   DiagnosticError = { fg = c.diag_error },  -- Hot pink #ff0066
-  DiagnosticUnderlineError = { sp = c.diag_error, undercurl = true },
+  DiagnosticUnderlineError = { bg = c.bg_diag_error },  -- Light pink background instead of undercurl
   DiagnosticSignError = { fg = c.diag_error, bg = c.bg },
   DiagnosticFloatingError = { fg = c.diag_error },
   DiagnosticVirtualTextError = { fg = c.diag_error },  -- No background
   
-  -- Warning diagnostics (fluorescent orange)
+  -- Warning diagnostics (fluorescent orange with light orange background)
   DiagnosticWarn = { fg = c.diag_warn },  -- Fluorescent orange #ff6600
-  DiagnosticUnderlineWarn = { sp = c.diag_warn, undercurl = true },
+  DiagnosticUnderlineWarn = { bg = c.bg_diag_warn },  -- Light orange background instead of undercurl
   DiagnosticSignWarn = { fg = c.diag_warn, bg = c.bg },
   DiagnosticFloatingWarn = { fg = c.diag_warn },
   DiagnosticVirtualTextWarn = { fg = c.diag_warn },  -- No background
   
-  -- Info diagnostics (bright fluorescent cyan)
+  -- Info diagnostics (bright fluorescent cyan with light cyan background)
   DiagnosticInfo = { fg = c.diag_info },  -- Bright cyan #00ccff
-  DiagnosticUnderlineInfo = { sp = c.diag_info, underline = true },
+  DiagnosticUnderlineInfo = { bg = c.bg_diag_info },  -- Light cyan background instead of underline
   DiagnosticSignInfo = { fg = c.diag_info, bg = c.bg },
   DiagnosticFloatingInfo = { fg = c.diag_info },
   DiagnosticVirtualTextInfo = { fg = c.diag_info },  -- No background
   
-  -- Hint diagnostics (softer fluorescent cyan)
+  -- Hint diagnostics (softer fluorescent cyan with very light cyan background)
   DiagnosticHint = { fg = c.diag_hint },  -- Soft cyan #66e0ff
-  DiagnosticUnderlineHint = { sp = c.diag_hint, underline = true },
+  DiagnosticUnderlineHint = { bg = c.bg_diag_hint },  -- Very light cyan background instead of underline
   DiagnosticSignHint = { fg = c.diag_hint, bg = c.bg },
   DiagnosticFloatingHint = { fg = c.diag_hint },
   DiagnosticVirtualTextHint = { fg = c.diag_hint },  -- No background

lua/settings.lua

@@ -56,15 +56,8 @@ vim.diagnostic.config({
       return string.format("%s: %s", diagnostic.source or "", diagnostic.message)
     end,
   },
-  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
+  signs = false,             -- Disable signs (redundant with background highlights and virtual text)
+  underline = true,          -- Use background highlights on problematic text
   update_in_insert = false,  -- Don't update diagnostics while typing
   severity_sort = true,      -- Sort by severity (errors first)
   float = {