feat: time-aware due dates, persistent undo, @return audit (#33)

* fix(plugin): allow command chaining with bar separator

Problem: :Pending|only failed because the command definition lacked the
bar attribute, causing | to be consumed as an argument.

Solution: Add bar = true to nvim_create_user_command so | is treated as
a command separator, matching fugitive's :Git behavior.

* refactor(buffer): remove opinionated window options

Problem: The plugin hardcoded number, relativenumber, wrap, spell,
signcolumn, foldcolumn, and cursorline in set_win_options, overriding
user preferences with no way to opt out.

Solution: Remove all cosmetic window options. Users who want them can
set them in after/ftplugin/pending.lua. Only conceallevel,
concealcursor, and winfixheight remain as functionally required.

* feat: time-aware due dates, persistent undo, @return audit

Problem: Due dates had no time component, the undo stack was lost on
restart and stored in a separate file, and many public functions lacked
required @return annotations.

Solution: Add YYYY-MM-DDThh:mm support across parse, views, recur,
complete, and init with time-aware overdue checks. Merge the undo stack
into the task store JSON so a single file holds all state. Add @return
nil annotations to all 27 void public functions across every module.

* 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.

* feat(complete): add info descriptions to omnifunc items

Problem: completion menu items had no description, making it hard to
distinguish between similar entries like date shorthands and recurrence
patterns.

Solution: return { word, info } tables from date_completions() and
recur_completions(), surfacing human-readable descriptions in the
completion popup.

* ci: format

spec/parse_spec.lua

@@ -323,6 +323,73 @@ describe('parse', function()
     end)
   end)
 
+  describe('resolve_date with time suffix', function()
+    local today = os.date('*t') --[[@as osdate]]
+    local tomorrow_str =
+      os.date('%Y-%m-%d', os.time({ year = today.year, month = today.month, day = today.day + 1 })) --[[@as string]]
+
+    it('resolves bare hour to T09:00', function()
+      local result = parse.resolve_date('tomorrow@9')
+      assert.are.equal(tomorrow_str .. 'T09:00', result)
+    end)
+
+    it('resolves bare military hour to T14:00', function()
+      local result = parse.resolve_date('tomorrow@14')
+      assert.are.equal(tomorrow_str .. 'T14:00', result)
+    end)
+
+    it('resolves H:MM to T09:30', function()
+      local result = parse.resolve_date('tomorrow@9:30')
+      assert.are.equal(tomorrow_str .. 'T09:30', result)
+    end)
+
+    it('resolves HH:MM (existing format) to T09:30', function()
+      local result = parse.resolve_date('tomorrow@09:30')
+      assert.are.equal(tomorrow_str .. 'T09:30', result)
+    end)
+
+    it('resolves 2pm to T14:00', function()
+      local result = parse.resolve_date('tomorrow@2pm')
+      assert.are.equal(tomorrow_str .. 'T14:00', result)
+    end)
+
+    it('resolves 9am to T09:00', function()
+      local result = parse.resolve_date('tomorrow@9am')
+      assert.are.equal(tomorrow_str .. 'T09:00', result)
+    end)
+
+    it('resolves 9:30pm to T21:30', function()
+      local result = parse.resolve_date('tomorrow@9:30pm')
+      assert.are.equal(tomorrow_str .. 'T21:30', result)
+    end)
+
+    it('resolves 12am to T00:00', function()
+      local result = parse.resolve_date('tomorrow@12am')
+      assert.are.equal(tomorrow_str .. 'T00:00', result)
+    end)
+
+    it('resolves 12pm to T12:00', function()
+      local result = parse.resolve_date('tomorrow@12pm')
+      assert.are.equal(tomorrow_str .. 'T12:00', result)
+    end)
+
+    it('rejects hour 24', function()
+      assert.is_nil(parse.resolve_date('tomorrow@24'))
+    end)
+
+    it('rejects 13am', function()
+      assert.is_nil(parse.resolve_date('tomorrow@13am'))
+    end)
+
+    it('rejects minute 60', function()
+      assert.is_nil(parse.resolve_date('tomorrow@9:60'))
+    end)
+
+    it('rejects alphabetic garbage', function()
+      assert.is_nil(parse.resolve_date('tomorrow@abc'))
+    end)
+  end)
+
   describe('command_add', function()
     it('parses simple text', function()
       local desc, meta = parse.command_add('Buy milk')