refactor: revert module namespace from canola back to oil

Problem: the canola rename creates unnecessary friction for users
migrating from stevearc/oil.nvim — every `require('oil')` call and
config reference must change.

Solution: revert all module paths, URL schemes, autocmd groups,
highlight groups, and filetype names back to `oil`. The repo stays
`canola.nvim` for identity; the code is a drop-in replacement.

lua/oil/log.lua

@@ -0,0 +1,126 @@
+local uv = vim.uv or vim.loop
+local levels_reverse = {}
+for k, v in pairs(vim.log.levels) do
+  levels_reverse[v] = k
+end
+
+local Log = {}
+
+---@type integer
+Log.level = vim.log.levels.WARN
+
+---@return string
+Log.get_logfile = function()
+  local fs = require('oil.fs')
+
+  local ok, stdpath = pcall(vim.fn.stdpath, 'log')
+  if not ok then
+    stdpath = vim.fn.stdpath('cache')
+  end
+  assert(type(stdpath) == 'string')
+  return fs.join(stdpath, 'oil.log')
+end
+
+---@param level integer
+---@param msg string
+---@param ... any[]
+---@return string
+local function format(level, msg, ...)
+  local args = vim.F.pack_len(...)
+  for i = 1, args.n do
+    local v = args[i]
+    if type(v) == 'table' then
+      args[i] = vim.inspect(v)
+    elseif v == nil then
+      args[i] = 'nil'
+    end
+  end
+  local ok, text = pcall(string.format, msg, vim.F.unpack_len(args))
+  -- TODO figure out how to get formatted time inside luv callback
+  -- local timestr = vim.fn.strftime("%Y-%m-%d %H:%M:%S")
+  local timestr = ''
+  if ok then
+    local str_level = levels_reverse[level]
+    return string.format('%s[%s] %s', timestr, str_level, text)
+  else
+    return string.format(
+      "%s[ERROR] error formatting log line: '%s' args %s",
+      timestr,
+      vim.inspect(msg),
+      vim.inspect(args)
+    )
+  end
+end
+
+---@param line string
+local function write(line)
+  -- This will be replaced during initialization
+end
+
+local initialized = false
+local function initialize()
+  if initialized then
+    return
+  end
+  initialized = true
+  local filepath = Log.get_logfile()
+
+  local stat = uv.fs_stat(filepath)
+  if stat and stat.size > 10 * 1024 * 1024 then
+    local backup = filepath .. '.1'
+    uv.fs_unlink(backup)
+    uv.fs_rename(filepath, backup)
+  end
+
+  local parent = vim.fs.dirname(filepath)
+  require('oil.fs').mkdirp(parent)
+
+  local logfile, openerr = io.open(filepath, 'a+')
+  if not logfile then
+    local err_msg = string.format('Failed to open oil.nvim log file: %s', openerr)
+    vim.notify(err_msg, vim.log.levels.ERROR)
+  else
+    write = function(line)
+      logfile:write(line)
+      logfile:write('\n')
+      logfile:flush()
+    end
+  end
+end
+
+---Override the file handler e.g. for tests
+---@param handler fun(line: string)
+function Log.set_handler(handler)
+  write = handler
+  initialized = true
+end
+
+function Log.log(level, msg, ...)
+  if Log.level <= level then
+    initialize()
+    local text = format(level, msg, ...)
+    write(text)
+  end
+end
+
+function Log.trace(...)
+  Log.log(vim.log.levels.TRACE, ...)
+end
+
+function Log.debug(...)
+  Log.log(vim.log.levels.DEBUG, ...)
+end
+
+function Log.info(...)
+  Log.log(vim.log.levels.INFO, ...)
+end
+
+function Log.warn(...)
+  Log.log(vim.log.levels.WARN, ...)
+end
+
+function Log.error(...)
+  Log.log(vim.log.levels.ERROR, ...)
+end
+
+return Log