feat(parse): flexible time parsing for @ suffix

Problem: the @HH:MM time suffix required zero-padded 24-hour format,
forcing users to write due:tomorrow@14:00 instead of due:tomorrow@2pm.

Solution: add normalize_time() that accepts bare hours (9, 14),
H:MM (9:30), am/pm (2pm, 9:30am, 12am), and existing HH:MM format,
normalizing all to canonical HH:MM on save.

lua/pending/parse.lua

@@ -36,6 +36,60 @@ local function is_valid_time(s)
   return hn >= 0 and hn <= 23 and mn >= 0 and mn <= 59
 end
 
+---@param s string
+---@return string|nil
+local function normalize_time(s)
+  local h, m, period
+
+  h, m, period = s:match('^(%d+):(%d%d)([ap]m)$')
+  if not h then
+    h, period = s:match('^(%d+)([ap]m)$')
+    if h then
+      m = '00'
+    end
+  end
+  if not h then
+    h, m = s:match('^(%d%d):(%d%d)$')
+  end
+  if not h then
+    h, m = s:match('^(%d):(%d%d)$')
+  end
+  if not h then
+    h = s:match('^(%d+)$')
+    if h then
+      m = '00'
+    end
+  end
+
+  if not h then
+    return nil
+  end
+
+  local hn = tonumber(h) --[[@as integer]]
+  local mn = tonumber(m) --[[@as integer]]
+
+  if period then
+    if hn < 1 or hn > 12 then
+      return nil
+    end
+    if period == 'am' then
+      hn = hn == 12 and 0 or hn
+    else
+      hn = hn == 12 and 12 or hn + 12
+    end
+  else
+    if hn < 0 or hn > 23 then
+      return nil
+    end
+  end
+
+  if mn < 0 or mn > 59 then
+    return nil
+  end
+
+  return string.format('%02d:%02d', hn, mn)
+end
+
 ---@param s string
 ---@return boolean
 local function is_valid_datetime(s)
@@ -100,9 +154,10 @@ end
 ---@param text string
 ---@return string|nil
 function M.resolve_date(text)
-  local date_input, time_suffix = text:match('^(.+)@(%d%d:%d%d)$')
+  local date_input, time_suffix = text:match('^(.+)@(.+)$')
   if time_suffix then
-    if not is_valid_time(time_suffix) then
+    time_suffix = normalize_time(time_suffix)
+    if not time_suffix then
       return nil
     end
   else