merge: resolve conflict with origin/main

Problem: the single dev shell mixed dev tooling (linters, test runner)
with preset compiler tools, causing heavy rebuilds (e.g. Chromium for
`mermaid-cli`) for contributors who only need the dev tools.

Solution: extract dev tooling into a shared `devTools` list and expose
two shells — `default` for development and `presets` for running all
built-in preset compilers (`typst`, `texliveMedium`, `tectonic`,
`pandoc`, `asciidoctor`, `quarto`, `plantuml`, `mermaid-cli`).

flake.nix

@@ -19,8 +19,7 @@
     {
       formatter = forEachSystem (pkgs: pkgs.nixfmt-tree);
 
-      devShells = forEachSystem (
-        pkgs:
+      devShells = forEachSystem (pkgs:
         let
           devTools = [
             (pkgs.luajit.withPackages (
@@ -51,7 +50,6 @@
               pkgs.mermaid-cli
             ];
           };
-        }
-      );
+        });
     };
 }

lua/preview/presets.lua

@@ -115,24 +115,6 @@ local function parse_asciidoctor(output)
   return diagnostics
 end
 
----@param output string
----@return preview.Diagnostic[]
-local function parse_mermaid(output)
-  local lnum = output:match('Parse error on line (%d+)')
-  if not lnum then
-    return {}
-  end
-  local msg = output:match('(Expecting .+)') or 'parse error'
-  return {
-    {
-      lnum = tonumber(lnum) - 1,
-      col = 0,
-      message = msg,
-      severity = vim.diagnostic.severity.ERROR,
-    },
-  }
-end
-
 ---@type preview.ProviderConfig
 M.typst = {
   ft = 'typst',
@@ -331,7 +313,19 @@ M.mermaid = {
     return (ctx.file:gsub('%.mmd$', '.svg'))
   end,
   error_parser = function(output)
-    return parse_mermaid(output)
+    local diagnostics = {}
+    for line in output:gmatch('[^\r\n]+') do
+      local lnum = line:match('^%s*Parse error on line (%d+)')
+      if lnum then
+        table.insert(diagnostics, {
+          lnum = tonumber(lnum) - 1,
+          col = 0,
+          message = line,
+          severity = vim.diagnostic.severity.ERROR,
+        })
+      end
+    end
+    return diagnostics
   end,
   clean = function(ctx)
     return { 'rm', '-f', (ctx.file:gsub('%.mmd$', '.svg')) }