feat(init): spawn next task on recurring task completion

Problem: completing a recurring task does not create the next
occurrence, and :Pending add does not pass recurrence fields.

Solution: in toggle_complete(), detect recurrence and spawn a new
pending task with the next due date. Wire rec/rec_mode through the
add() command path.

lua/pending/init.lua

@@ -127,6 +127,20 @@ function M.toggle_complete()
   if task.status == 'done' then
     store.update(id, { status = 'pending', ['end'] = vim.NIL })
   else
+    if task.recur and task.due then
+      local recur = require('pending.recur')
+      local mode = task.recur_mode or 'scheduled'
+      local base = mode == 'completion' and os.date('%Y-%m-%d') --[[@as string]] or task.due
+      local next_date = recur.next_due(base, task.recur, mode)
+      store.add({
+        description = task.description,
+        category = task.category,
+        priority = task.priority,
+        due = next_date,
+        recur = task.recur,
+        recur_mode = task.recur_mode,
+      })
+    end
     store.update(id, { status = 'done' })
   end
   store.save()
@@ -219,6 +233,8 @@ function M.add(text)
     description = description,
     category = metadata.cat,
     due = metadata.due,
+    recur = metadata.rec,
+    recur_mode = metadata.rec_mode,
   })
   store.save()
   local bufnr = buffer.bufnr()
@@ -320,6 +336,7 @@ end
 function M.show_help()
   local cfg = require('pending.config').get()
   local dk = cfg.date_syntax or 'due'
+  local rk = cfg.recur_syntax or 'rec'
   local lines = {
     'pending.nvim keybindings',
     '',
@@ -344,14 +361,21 @@ function M.show_help()
     'Inline metadata (on new lines before :w):',
     '  ' .. dk .. ':YYYY-MM-DD    Set due date',
     '  cat:Name          Set category',
+    '  ' .. rk .. ':pattern       Set recurrence',
     '',
     'Due date input:',
-    '  today, tomorrow, +Nd, mon-sun',
+    '  today, tomorrow, yesterday, +Nd, +Nw, +Nm',
+    '  -Nd, -Nw, mon-sun, jan-dec, 1st-31st',
+    '  eod, eow, eom, eoq, eoy, sow, som, soq, soy',
+    '  later, someday',
     '  Empty input clears due date',
     '',
-    'Highlights:',
+    'Recurrence patterns:',
-    '  PendingOverdue   overdue tasks (red)',
+    '  daily, weekdays, weekly, biweekly',
-    '  PendingPriority  [!] urgent tasks',
+    '  monthly, quarterly, yearly, Nd, Nw, Nm, Ny',
+    '  Prefix ! for completion-based (e.g. !weekly)',
+    '',
+    'Completion: <C-x><C-o> after due:, cat:, rec:',
     '',
     'Press q or <Esc> to close',
   }