feat(plugins): integrate ruff via mason-tool-installer and configure Python formatting

lua/plugins/conform.lua

@@ -79,6 +79,15 @@ end
 
 ---@type LazySpec
 return {
+  -- ruff is both the import sorter and the formatter used for python below
+  {
+    "WhoIsSethDaniel/mason-tool-installer.nvim",
+    optional = true,
+    opts = function(_, opts)
+      opts.ensure_installed = require("astrocore").list_insert_unique(opts.ensure_installed, { "ruff" })
+    end,
+  },
+  {
     "stevearc/conform.nvim",
     init = function()
       vim.api.nvim_create_autocmd("BufWritePre", {
@@ -92,6 +101,12 @@ return {
       })
     end,
     opts = function(_, opts)
+      -- Python: ruff sorts imports (I001), then reformats. ruff always emits
+      -- 4-space indentation, so mixed tab/space indentation is normalized on
+      -- save instead of surviving to raise TabError at runtime.
+      if not opts.formatters_by_ft then opts.formatters_by_ft = {} end
+      opts.formatters_by_ft.python = { "ruff_organize_imports", "ruff_format" }
+
       -- Skip format-on-save for JavaScript buffers (.js/.mjs/.cjs); manual
       -- :Format / <Leader>lf still works. Wraps the astrocommunity pack's
       -- format_on_save so its autoformat toggle handling is preserved.
@@ -102,4 +117,5 @@ return {
         return pack_format_on_save
       end
     end,
+  },
 }