refactor(config): nest view settings under view key (#103)

Problem: View-related config fields (`default_view`, `eol_format`,
`category_order`, `folding`) are scattered as top-level siblings
alongside unrelated fields like `data_path` and `date_syntax`.

Solution: Group them under a `view` table with per-view sub-tables:
`view.default`, `view.eol_format`, `view.category.order`,
`view.category.folding`, and `view.queue` (empty, ready for #100).
Update all call sites, tests, and vimdoc.

lua/pending/config.lua

@@ -49,22 +49,31 @@
 ---@field next_task? string|false
 ---@field prev_task? string|false
 
+---@class pending.CategoryViewConfig
+---@field order? string[]
+---@field folding? boolean|pending.FoldingConfig
+
+---@class pending.QueueViewConfig
+
+---@class pending.ViewConfig
+---@field default? 'category'|'priority'
+---@field eol_format? string
+---@field category? pending.CategoryViewConfig
+---@field queue? pending.QueueViewConfig
+
 ---@class pending.Config
 ---@field data_path string
----@field default_view 'category'|'priority'
 ---@field default_category string
 ---@field date_format string
 ---@field date_syntax string
 ---@field recur_syntax string
 ---@field someday_date string
 ---@field input_date_formats? string[]
----@field category_order? string[]
 ---@field drawer_height? integer
 ---@field debug? boolean
 ---@field keymaps pending.Keymaps
----@field folding? boolean|pending.FoldingConfig
+---@field view pending.ViewConfig
 ---@field sync? pending.SyncConfig
----@field eol_format? string
 ---@field icons pending.Icons
 
 ---@class pending.config
@@ -73,15 +82,20 @@ local M = {}
 ---@type pending.Config
 local defaults = {
   data_path = vim.fn.stdpath('data') .. '/pending/tasks.json',
-  default_view = 'category',
   default_category = 'Todo',
   date_format = '%b %d',
   date_syntax = 'due',
   recur_syntax = 'rec',
   someday_date = '9999-12-30',
-  eol_format = '%c  %r  %d',
-  folding = true,
-  category_order = {},
+  view = {
+    default = 'category',
+    eol_format = '%c  %r  %d',
+    category = {
+      order = {},
+      folding = true,
+    },
+    queue = {},
+  },
   keymaps = {
     close = 'q',
     toggle = '<CR>',
@@ -132,7 +146,7 @@ end
 
 ---@return pending.ResolvedFolding
 function M.resolve_folding()
-  local raw = M.get().folding
+  local raw = M.get().view.category.folding
   if raw == false then
     return { enabled = false, foldtext = false }
   elseif raw == true or raw == nil then