build: replace luacheck with selene, add nix devshell and pre-commit (#20)

* build: replace luacheck with selene

Problem: luacheck is unmaintained (last release 2018) and required
suppressing four warning classes to avoid false positives. It also
lacks first-class vim/neovim awareness.

Solution: switch to selene with std='vim' for vim-aware linting.
Replace the luacheck CI job with selene, update the Makefile lint
target, and delete .luacheckrc.

* build: add nix devshell and pre-commit hooks

Problem: oil.nvim had no reproducible dev environment. The .envrc
set up a Python venv for the now-removed docgen pipeline, and there
were no pre-commit hooks for local formatting checks.

Solution: add flake.nix with stylua, selene, and prettier in the
devshell. Replace the stale Python .envrc with 'use flake'. Add
.pre-commit-config.yaml with stylua and prettier hooks matching
other plugins in the repo collection.

* fix: format with stylua

* build(selene): configure lints and add inline suppressions

Problem: selene fails on 5 errors and 3 warnings from upstream code
patterns that are intentional (mixed tables in config API, unused
callback parameters, identical if branches for readability).

Solution: globally allow mixed_table and unused_variable (high volume,
inherent to the codebase design). Add inline selene:allow directives
for the 8 remaining issues: if_same_then_else (4), mismatched_arg_count
(1), empty_if (2), global_usage (1). Remove .envrc from tracking.

* build: switch typecheck action to mrcjkb/lua-typecheck-action

Problem: oil.nvim used stevearc/nvim-typecheck-action, which required
cloning the action repo locally for the Makefile lint target. All
other plugins in the collection use mrcjkb/lua-typecheck-action.

Solution: swap to mrcjkb/lua-typecheck-action@v0 for consistency.
Remove the nvim-typecheck-action git clone from the Makefile and
.gitignore. Drop LuaLS from the local lint target since it requires
a full language server install — CI handles it.

lua/oil/mutator/confirmation.lua

@@ -1,7 +1,7 @@
-local columns = require("oil.columns")
-local config = require("oil.config")
-local layout = require("oil.layout")
-local util = require("oil.util")
+local columns = require('oil.columns')
+local config = require('oil.config')
+local layout = require('oil.layout')
+local util = require('oil.util')
 local M = {}
 
 ---@param actions oil.Action[]
@@ -12,17 +12,17 @@ local function is_simple_edit(actions)
   local num_move = 0
   for _, action in ipairs(actions) do
     -- If there are any deletes, it is not a simple edit
-    if action.type == "delete" then
+    if action.type == 'delete' then
       return false
-    elseif action.type == "create" then
+    elseif action.type == 'create' then
       num_create = num_create + 1
-    elseif action.type == "copy" then
+    elseif action.type == 'copy' then
       num_copy = num_copy + 1
       -- Cross-adapter copies are not simple
       if util.parse_url(action.src_url) ~= util.parse_url(action.dest_url) then
         return false
       end
-    elseif action.type == "move" then
+    elseif action.type == 'move' then
       num_move = num_move + 1
       -- Cross-adapter moves are not simple
       if util.parse_url(action.src_url) ~= util.parse_url(action.dest_url) then
@@ -46,10 +46,10 @@ end
 ---@param lines string[]
 local function render_lines(winid, bufnr, lines)
   util.render_text(bufnr, lines, {
-    v_align = "top",
-    h_align = "left",
+    v_align = 'top',
+    h_align = 'left',
     winid = winid,
-    actions = { "[Y]es", "[N]o" },
+    actions = { '[Y]es', '[N]o' },
   })
 end
 
@@ -70,48 +70,48 @@ M.show = vim.schedule_wrap(function(actions, should_confirm, cb)
 
   -- Create the buffer
   local bufnr = vim.api.nvim_create_buf(false, true)
-  vim.bo[bufnr].bufhidden = "wipe"
+  vim.bo[bufnr].bufhidden = 'wipe'
   local lines = {}
   local max_line_width = 0
   for _, action in ipairs(actions) do
     local adapter = util.get_adapter_for_action(action)
     local line
-    if action.type == "change" then
+    if action.type == 'change' then
       ---@cast action oil.ChangeAction
       line = columns.render_change_action(adapter, action)
     else
       line = adapter.render_action(action)
     end
     -- We can't handle lines with newlines in them
-    line = line:gsub("\n", "")
+    line = line:gsub('\n', '')
     table.insert(lines, line)
     local line_width = vim.api.nvim_strwidth(line)
     if line_width > max_line_width then
       max_line_width = line_width
     end
   end
-  table.insert(lines, "")
+  table.insert(lines, '')
 
   -- Create the floating window
   local width, height = layout.calculate_dims(max_line_width, #lines + 1, config.confirmation)
   local ok, winid = pcall(vim.api.nvim_open_win, bufnr, true, {
-    relative = "editor",
+    relative = 'editor',
     width = width,
     height = height,
     row = math.floor((layout.get_editor_height() - height) / 2),
     col = math.floor((layout.get_editor_width() - width) / 2),
     zindex = 152, -- render on top of the floating window title
-    style = "minimal",
+    style = 'minimal',
     border = config.confirmation.border,
   })
   if not ok then
-    vim.notify(string.format("Error showing oil preview window: %s", winid), vim.log.levels.ERROR)
+    vim.notify(string.format('Error showing oil preview window: %s', winid), vim.log.levels.ERROR)
     cb(false)
   end
-  vim.bo[bufnr].filetype = "oil_preview"
-  vim.bo[bufnr].syntax = "oil_preview"
+  vim.bo[bufnr].filetype = 'oil_preview'
+  vim.bo[bufnr].syntax = 'oil_preview'
   for k, v in pairs(config.confirmation.win_options) do
-    vim.api.nvim_set_option_value(k, v, { scope = "local", win = winid })
+    vim.api.nvim_set_option_value(k, v, { scope = 'local', win = winid })
   end
 
   render_lines(winid, bufnr, lines)
@@ -137,7 +137,7 @@ M.show = vim.schedule_wrap(function(actions, should_confirm, cb)
   end
   cancel = make_callback(false)
   confirm = make_callback(true)
-  vim.api.nvim_create_autocmd("BufLeave", {
+  vim.api.nvim_create_autocmd('BufLeave', {
     callback = function()
       cancel()
     end,
@@ -145,7 +145,7 @@ M.show = vim.schedule_wrap(function(actions, should_confirm, cb)
     nested = true,
     buffer = bufnr,
   })
-  vim.api.nvim_create_autocmd("WinLeave", {
+  vim.api.nvim_create_autocmd('WinLeave', {
     callback = function()
       cancel()
     end,
@@ -154,12 +154,12 @@ M.show = vim.schedule_wrap(function(actions, should_confirm, cb)
   })
   table.insert(
     autocmds,
-    vim.api.nvim_create_autocmd("VimResized", {
+    vim.api.nvim_create_autocmd('VimResized', {
       callback = function()
         if vim.api.nvim_win_is_valid(winid) then
           width, height = layout.calculate_dims(max_line_width, #lines, config.confirmation)
           vim.api.nvim_win_set_config(winid, {
-            relative = "editor",
+            relative = 'editor',
             width = width,
             height = height,
             row = math.floor((layout.get_editor_height() - height) / 2),
@@ -173,17 +173,17 @@ M.show = vim.schedule_wrap(function(actions, should_confirm, cb)
   )
 
   -- We used to use [C]ancel to cancel, so preserve the old keymap
-  local cancel_keys = { "n", "N", "c", "C", "q", "<C-c>", "<Esc>" }
+  local cancel_keys = { 'n', 'N', 'c', 'C', 'q', '<C-c>', '<Esc>' }
   for _, cancel_key in ipairs(cancel_keys) do
-    vim.keymap.set("n", cancel_key, function()
+    vim.keymap.set('n', cancel_key, function()
       cancel()
     end, { buffer = bufnr, nowait = true })
   end
 
   -- We used to use [O]k to confirm, so preserve the old keymap
-  local confirm_keys = { "y", "Y", "o", "O" }
+  local confirm_keys = { 'y', 'Y', 'o', 'O' }
   for _, confirm_key in ipairs(confirm_keys) do
-    vim.keymap.set("n", confirm_key, function()
+    vim.keymap.set('n', confirm_key, function()
       confirm()
     end, { buffer = bufnr, nowait = true })
   end