fix(sync): replace cryptic sigil counters with readable output

Problem: sync summaries used unexplained sigils (`+/-/~` and `!`) that
conveyed no meaning, mixed symbol and prose formats across operations,
and `gcal push` silently swallowed failures with no aggregate counter.

Solution: replace all summary `log.info` calls with a shared
`fmt_counts` helper that formats `N label` pairs separated by ` | `,
suppresses zero counts, and falls back to "nothing to do". Add a
`failed` counter to `gcal.push` to surface errors previously only
emitted as individual warnings.

lua/pending/sync/gcal.lua

@@ -154,6 +154,21 @@ local function unlink_remote(task, extra, now_ts)
   task.modified = now_ts
 end
 
+---@param parts {[1]: integer, [2]: string}[]
+---@return string
+local function fmt_counts(parts)
+  local items = {}
+  for _, p in ipairs(parts) do
+    if p[1] > 0 then
+      table.insert(items, p[1] .. ' ' .. p[2])
+    end
+  end
+  if #items == 0 then
+    return 'nothing to do'
+  end
+  return table.concat(items, ' | ')
+end
+
 ---@param callback fun(access_token: string): nil
 local function with_token(callback)
   oauth.async(function()
@@ -176,7 +191,7 @@ function M.push()
 
     local s = require('pending').store()
     local now_ts = os.date('!%Y-%m-%dT%H:%M:%SZ') --[[@as string]]
-    local created, updated, deleted = 0, 0, 0
+    local created, updated, deleted, failed = 0, 0, 0, 0
 
     for _, task in ipairs(s:tasks()) do
       local extra = task._extra or {}
@@ -197,6 +212,7 @@ function M.push()
             delete_event(access_token, cal_id --[[@as string]], event_id --[[@as string]])
           if del_err then
             log.warn('gcal delete failed: ' .. del_err)
+            failed = failed + 1
           else
             unlink_remote(task, extra, now_ts)
             deleted = deleted + 1
@@ -214,6 +230,7 @@ function M.push()
           local upd_err = update_event(access_token, cal_id, event_id, task)
           if upd_err then
             log.warn('gcal update failed: ' .. upd_err)
+            failed = failed + 1
           else
             updated = updated + 1
           end
@@ -221,10 +238,12 @@ function M.push()
           local lid, lid_err = find_or_create_calendar(access_token, cat, calendars)
           if lid_err or not lid then
             log.warn('gcal calendar failed: ' .. (lid_err or 'unknown'))
+            failed = failed + 1
           else
             local new_id, create_err = create_event(access_token, lid, task)
             if create_err then
               log.warn('gcal create failed: ' .. create_err)
+              failed = failed + 1
             elseif new_id then
               if not task._extra then
                 task._extra = {}
@@ -245,7 +264,15 @@ function M.push()
     if buffer.bufnr() and vim.api.nvim_buf_is_valid(buffer.bufnr()) then
       buffer.render(buffer.bufnr())
     end
-    log.info(string.format('Google Calendar pushed — +%d ~%d -%d', created, updated, deleted))
+    log.info(
+      'gcal push: '
+        .. fmt_counts({
+          { created, 'added' },
+          { updated, 'updated' },
+          { deleted, 'removed' },
+          { failed, 'failed' },
+        })
+    )
   end)
 end