feat(views): make queue view sort order configurable (#154)

Problem: the queue/priority view sort in `sort_tasks_priority()` uses a
hardcoded tiebreak chain (status, priority, due, order, id). Users who
care more about due dates than priority have no way to reorder it.

Solution: add `view.queue.sort` config field (string[]) that defines an
ordered tiebreak chain. `build_queue_comparator()` maps each key to a
comparison function and returns a single comparator. Unknown keys emit a
`log.warn`. The default matches the previous hardcoded behavior.

spec/views_spec.lua

@@ -529,5 +529,83 @@ describe('views', function()
       end
       assert.is_nil(task_meta.recur)
     end)
+
+    it('sorts by due before priority when sort config is reordered', function()
+      vim.g.pending = {
+        data_path = tmpdir .. '/tasks.json',
+        view = { queue = { sort = { 'status', 'due', 'priority', 'order', 'id' } } },
+      }
+      config.reset()
+      s:add({ description = 'High no due', category = 'Work', priority = 2 })
+      s:add({ description = 'Low with due', category = 'Work', priority = 0, due = '2050-01-01' })
+      local lines, meta = views.priority_view(s:active_tasks())
+      local due_row, nodue_row
+      for i, m in ipairs(meta) do
+        if m.type == 'task' then
+          if lines[i]:find('Low with due') then
+            due_row = i
+          elseif lines[i]:find('High no due') then
+            nodue_row = i
+          end
+        end
+      end
+      assert.is_true(due_row < nodue_row)
+    end)
+
+    it('uses default sort when config sort is nil', function()
+      vim.g.pending = {
+        data_path = tmpdir .. '/tasks.json',
+        view = { queue = {} },
+      }
+      config.reset()
+      s:add({ description = 'Low', category = 'Work', priority = 0 })
+      s:add({ description = 'High', category = 'Work', priority = 1 })
+      local lines, meta = views.priority_view(s:active_tasks())
+      local high_row, low_row
+      for i, m in ipairs(meta) do
+        if m.type == 'task' then
+          if lines[i]:find('High') then
+            high_row = i
+          elseif lines[i]:find('Low') then
+            low_row = i
+          end
+        end
+      end
+      assert.is_true(high_row < low_row)
+    end)
+
+    it('ignores unknown sort keys with a warning', function()
+      vim.g.pending = {
+        data_path = tmpdir .. '/tasks.json',
+        view = { queue = { sort = { 'bogus', 'status', 'id' } } },
+      }
+      config.reset()
+      s:add({ description = 'A', category = 'Work' })
+      s:add({ description = 'B', category = 'Work' })
+      local lines = views.priority_view(s:active_tasks())
+      assert.is_true(#lines == 2)
+    end)
+
+    it('supports age sort key as alias for id', function()
+      vim.g.pending = {
+        data_path = tmpdir .. '/tasks.json',
+        view = { queue = { sort = { 'age' } } },
+      }
+      config.reset()
+      s:add({ description = 'Older', category = 'Work' })
+      s:add({ description = 'Newer', category = 'Work' })
+      local lines, meta = views.priority_view(s:active_tasks())
+      local older_row, newer_row
+      for i, m in ipairs(meta) do
+        if m.type == 'task' then
+          if lines[i]:find('Older') then
+            older_row = i
+          elseif lines[i]:find('Newer') then
+            newer_row = i
+          end
+        end
+      end
+      assert.is_true(older_row < newer_row)
+    end)
   end)
 end)