feat(parse): add rec: inline token parsing

Problem: the buffer parser does not recognize recurrence tokens,
so users cannot set recurrence rules inline.

Solution: add recur_key() helper and rec: token parsing in body()
and command_add(), with ! prefix handling for completion-based mode
and validation via recur.validate().

lua/pending/parse.lua

@@ -29,6 +29,11 @@ local function date_key()
   return config.get().date_syntax or 'due'
 end
 
+---@return string
+local function recur_key()
+  return config.get().recur_syntax or 'rec'
+end
+
 local weekday_map = {
   sun = 1,
   mon = 2,
@@ -259,7 +264,7 @@ end
 
 ---@param text string
 ---@return string description
----@return { due?: string, cat?: string } metadata
+---@return { due?: string, cat?: string, rec?: string, rec_mode?: 'scheduled'|'completion' } metadata
 function M.body(text)
   local tokens = {}
   for token in text:gmatch('%S+') do
@@ -269,8 +274,10 @@ function M.body(text)
   local metadata = {}
   local i = #tokens
   local dk = date_key()
+  local rk = recur_key()
   local date_pattern_strict = '^' .. vim.pesc(dk) .. ':(%d%d%d%d%-%d%d%-%d%d)$'
   local date_pattern_any = '^' .. vim.pesc(dk) .. ':(.+)$'
+  local rec_pattern = '^' .. vim.pesc(rk) .. ':(%S+)$'
 
   while i >= 1 do
     local token = tokens[i]
@@ -305,7 +312,25 @@ function M.body(text)
           metadata.cat = cat_val
           i = i - 1
         else
-          break
+          local rec_val = token:match(rec_pattern)
+          if rec_val then
+            if metadata.rec then
+              break
+            end
+            local recur = require('pending.recur')
+            local raw_spec = rec_val
+            if raw_spec:sub(1, 1) == '!' then
+              metadata.rec_mode = 'completion'
+              raw_spec = raw_spec:sub(2)
+            end
+            if not recur.validate(raw_spec) then
+              break
+            end
+            metadata.rec = raw_spec
+            i = i - 1
+          else
+            break
+          end
         end
       end
     end
@@ -322,7 +347,7 @@ end
 
 ---@param text string
 ---@return string description
----@return { due?: string, cat?: string } metadata
+---@return { due?: string, cat?: string, rec?: string, rec_mode?: 'scheduled'|'completion' } metadata
 function M.command_add(text)
   local cat_prefix = text:match('^(%S.-):%s')
   if cat_prefix then