feat(diff): propagate recurrence through buffer reconciliation

Problem: the diff layer does not extract or apply recurrence fields,
so rec: tokens written in the buffer are silently ignored on :w.

Solution: add rec and rec_mode to ParsedEntry, extract them in
parse_buffer(), and pass them through create and update paths in
apply().

spec/diff_spec.lua

@@ -69,6 +69,25 @@ describe('diff', function()
       assert.are.equal('Work', result[2].category)
     end)
 
+    it('extracts rec: token from buffer line', function()
+      local lines = {
+        '## Inbox',
+        '/1/- [ ] Take trash out rec:weekly',
+      }
+      local result = diff.parse_buffer(lines)
+      assert.are.equal('weekly', result[2].rec)
+    end)
+
+    it('extracts rec: with completion mode', function()
+      local lines = {
+        '## Inbox',
+        '/1/- [ ] Water plants rec:!daily',
+      }
+      local result = diff.parse_buffer(lines)
+      assert.are.equal('daily', result[2].rec)
+      assert.are.equal('completion', result[2].rec_mode)
+    end)
+
     it('inline due: token is parsed', function()
       local lines = {
         '## Inbox',
@@ -206,6 +225,60 @@ describe('diff', function()
       assert.is_nil(task.due)
     end)
 
+    it('stores recur field on new tasks from buffer', function()
+      local lines = {
+        '## Inbox',
+        '- [ ] Take out trash rec:weekly',
+      }
+      diff.apply(lines)
+      store.unload()
+      store.load()
+      local tasks = store.active_tasks()
+      assert.are.equal(1, #tasks)
+      assert.are.equal('weekly', tasks[1].recur)
+    end)
+
+    it('updates recur field when changed inline', function()
+      store.add({ description = 'Task', recur = 'daily' })
+      store.save()
+      local lines = {
+        '## Todo',
+        '/1/- [ ] Task rec:weekly',
+      }
+      diff.apply(lines)
+      store.unload()
+      store.load()
+      local task = store.get(1)
+      assert.are.equal('weekly', task.recur)
+    end)
+
+    it('clears recur when token removed from line', function()
+      store.add({ description = 'Task', recur = 'daily' })
+      store.save()
+      local lines = {
+        '## Todo',
+        '/1/- [ ] Task',
+      }
+      diff.apply(lines)
+      store.unload()
+      store.load()
+      local task = store.get(1)
+      assert.is_nil(task.recur)
+    end)
+
+    it('parses rec: with completion mode prefix', function()
+      local lines = {
+        '## Inbox',
+        '- [ ] Water plants rec:!weekly',
+      }
+      diff.apply(lines)
+      store.unload()
+      store.load()
+      local tasks = store.active_tasks()
+      assert.are.equal('weekly', tasks[1].recur)
+      assert.are.equal('completion', tasks[1].recur_mode)
+    end)
+
     it('clears priority when [N] is removed from buffer line', function()
       store.add({ description = 'Task name', priority = 1 })
       store.save()