feat(config): add icons table with unicode defaults

lua/pending/config.lua

@@ -1,3 +1,12 @@
+---@class pending.Icons
+---@field pending string
+---@field done string
+---@field priority string
+---@field header string
+---@field due string
+---@field recur string
+---@field category string
+
 ---@class pending.GcalConfig
 ---@field calendar? string
 ---@field credentials_path? string
@@ -38,6 +47,7 @@
 ---@field keymaps pending.Keymaps
 ---@field sync? pending.SyncConfig
 ---@field gcal? pending.GcalConfig
+---@field icons pending.Icons
 
 ---@class pending.config
 local M = {}
@@ -71,6 +81,15 @@ local defaults = {
     prev_task = '[t',
   },
   sync = {},
+  icons = {
+    pending  = '○',
+    done     = '✓',
+    priority = '●',
+    header   = '▸',
+    due      = '·',
+    recur    = '↺',
+    category = '#',
+  },
 }
 
 ---@type pending.Config?