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/adapters/files/permissions.lua

@@ -0,0 +1,103 @@
+local M = {}
+
+---@param exe_modifier false|string
+---@param num integer
+---@return string
+local function perm_to_str(exe_modifier, num)
+  local str = (bit.band(num, 4) ~= 0 and 'r' or '-') .. (bit.band(num, 2) ~= 0 and 'w' or '-')
+  if exe_modifier then
+    if bit.band(num, 1) ~= 0 then
+      return str .. exe_modifier
+    else
+      return str .. exe_modifier:upper()
+    end
+  else
+    return str .. (bit.band(num, 1) ~= 0 and 'x' or '-')
+  end
+end
+
+---@param mode integer
+---@return string
+M.mode_to_str = function(mode)
+  local extra = bit.rshift(mode, 9)
+  return perm_to_str(bit.band(extra, 4) ~= 0 and 's', bit.rshift(mode, 6))
+    .. perm_to_str(bit.band(extra, 2) ~= 0 and 's', bit.rshift(mode, 3))
+    .. perm_to_str(bit.band(extra, 1) ~= 0 and 't', mode)
+end
+
+---@param mode integer
+---@return string
+M.mode_to_octal_str = function(mode)
+  local mask = 7
+  return tostring(bit.band(mask, bit.rshift(mode, 9)))
+    .. tostring(bit.band(mask, bit.rshift(mode, 6)))
+    .. tostring(bit.band(mask, bit.rshift(mode, 3)))
+    .. tostring(bit.band(mask, mode))
+end
+
+---@param str string String of 3 characters
+---@return nil|integer
+local function str_to_mode(str)
+  local r, w, x = unpack(vim.split(str, '', {}))
+  local mode = 0
+  if r == 'r' then
+    mode = bit.bor(mode, 4)
+  elseif r ~= '-' then
+    return nil
+  end
+  if w == 'w' then
+    mode = bit.bor(mode, 2)
+  elseif w ~= '-' then
+    return nil
+  end
+  -- t means sticky and executable
+  -- T means sticky, not executable
+  -- s means setuid/setgid and executable
+  -- S means setuid/setgid and not executable
+  if x == 'x' or x == 't' or x == 's' then
+    mode = bit.bor(mode, 1)
+  elseif x ~= '-' and x ~= 'T' and x ~= 'S' then
+    return nil
+  end
+  return mode
+end
+
+---@param perm string
+---@return integer
+local function parse_extra_bits(perm)
+  perm = perm:lower()
+  local mode = 0
+  if perm:sub(3, 3) == 's' then
+    mode = bit.bor(mode, 4)
+  end
+  if perm:sub(6, 6) == 's' then
+    mode = bit.bor(mode, 2)
+  end
+  if perm:sub(9, 9) == 't' then
+    mode = bit.bor(mode, 1)
+  end
+  return mode
+end
+
+---@param line string
+---@return nil|integer
+---@return nil|string
+M.parse = function(line)
+  local strval, rem = line:match('^([r%-][w%-][xsS%-][r%-][w%-][xsS%-][r%-][w%-][xtT%-])%s*(.*)$')
+  if not strval then
+    return
+  end
+  local user_mode = str_to_mode(strval:sub(1, 3))
+  local group_mode = str_to_mode(strval:sub(4, 6))
+  local any_mode = str_to_mode(strval:sub(7, 9))
+  local extra = parse_extra_bits(strval)
+  if not user_mode or not group_mode or not any_mode then
+    return
+  end
+  local mode = bit.bor(bit.lshift(user_mode, 6), bit.lshift(group_mode, 3))
+  mode = bit.bor(mode, any_mode)
+  mode = bit.bor(mode, bit.lshift(extra, 9))
+  return mode, rem
+end
+
+return M