feat(presets): add pdflatex preset

Adds a direct pdflatex preset for users who want single-pass
compilation without latexmk orchestration. Uses -file-line-error
for parseable diagnostics and reuses the existing parse_latexmk
error parser since both emit the same file:line: message format.

lua/preview/presets.lua

@@ -137,6 +137,22 @@ M.latex = {
   open = true,
 }
 
+---@type preview.ProviderConfig
+M.pdflatex = {
+  ft = 'tex',
+  cmd = { 'pdflatex' },
+  args = function(ctx)
+    return { '-interaction=nonstopmode', '-file-line-error', '-synctex=1', ctx.file }
+  end,
+  output = function(ctx)
+    return (ctx.file:gsub('%.tex$', '.pdf'))
+  end,
+  error_parser = function(output)
+    return parse_latexmk(output)
+  end,
+  open = true,
+}
+
 ---@type preview.ProviderConfig
 M.markdown = {
   ft = 'markdown',