fix: resolve selene lint warnings and errors

Problem: unused variables (undo_state, sha_result, date match
captures) and duplicate if/else branches in gcal sync triggered
selene warnings and errors.

Solution: prefix unused state with underscore, simplify date
validation to a single pattern match, remove dead sha_result
call, and merge duplicate event deletion branches into a single
condition.

lua/todo/init.lua

@@ -7,7 +7,7 @@ local store = require('todo.store')
 local M = {}
 
 ---@type todo.Task[]?
-local undo_state = nil
+local _undo_state = nil
 
 ---@return integer bufnr
 function M.open()
@@ -46,7 +46,7 @@ end
 ---@param bufnr integer
 function M._on_write(bufnr)
   local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
-  undo_state = store.active_tasks()
+  _undo_state = store.active_tasks()
   diff.apply(lines)
   buffer.render(bufnr)
 end
@@ -113,8 +113,7 @@ function M.prompt_date()
     end
     local due = input ~= '' and input or nil
     if due then
-      local y, m, d = due:match('^(%d%d%d%d)-(%d%d)-(%d%d)$')
-      if not y then
+      if not due:match('^%d%d%d%d%-%d%d%-%d%d$') then
         vim.notify('Invalid date format. Use YYYY-MM-DD.', vim.log.levels.ERROR)
         return
       end

lua/todo/sync/gcal.lua

@@ -199,7 +199,6 @@ function M.authorize()
   end
   local code_verifier = table.concat(verifier)
 
-  local sha_result = vim.system({ 'printf', '%s', code_verifier }, { text = true }):wait()
   local sha_pipe = vim
     .system({
       'sh',
@@ -401,7 +400,14 @@ function M.sync()
     local extra = task._extra or {}
     local event_id = extra._gcal_event_id
 
-    if (task.status == 'done' or task.status == 'deleted') and event_id then
+    local should_delete = event_id
+      and (
+        task.status == 'done'
+        or task.status == 'deleted'
+        or (task.status == 'pending' and not task.due)
+      )
+
+    if should_delete then
       local del_err = delete_event(access_token, calendar_id, event_id)
       if not del_err then
         extra._gcal_event_id = nil
@@ -430,18 +436,6 @@ function M.sync()
           created = created + 1
         end
       end
-    elseif task.status == 'pending' and not task.due and event_id then
-      local del_err = delete_event(access_token, calendar_id, event_id)
-      if not del_err then
-        extra._gcal_event_id = nil
-        if next(extra) == nil then
-          task._extra = nil
-        else
-          task._extra = extra
-        end
-        task.modified = os.date('!%Y-%m-%dT%H:%M:%SZ')
-        deleted = deleted + 1
-      end
     end
   end
 

spec/parse_spec.lua

@@ -103,7 +103,7 @@ describe('parse', function()
     end)
 
     it('ignores lowercase prefix', function()
-      local desc, meta = parse.command_add('hello: world')
+      local desc, _ = parse.command_add('hello: world')
       assert.are.equal('hello: world', desc)
     end)