refactor(config): remove legacy gcal top-level config key

Problem: the gcal migration shim silently accepted vim.g.pending = { gcal
= {...} } and copied it to sync.gcal, adding complexity and a deprecated
API surface.

Solution: remove the migration block in config.get(), drop the cfg.gcal
fallback in gcal_config(), delete the two migration tests, and clean up
the vimdoc references. Callers must now use sync.gcal directly.

lua/pending/config.lua

@@ -45,7 +45,6 @@
 ---@field debug? boolean
 ---@field keymaps pending.Keymaps
 ---@field sync? pending.SyncConfig
----@field gcal? pending.GcalConfig
 ---@field icons pending.Icons
 
 ---@class pending.config
@@ -101,10 +100,6 @@ function M.get()
   end
   local user = vim.g.pending or {}
   _resolved = vim.tbl_deep_extend('force', defaults, user)
-  if _resolved.gcal and not (_resolved.sync and _resolved.sync.gcal) then
-    _resolved.sync = _resolved.sync or {}
-    _resolved.sync.gcal = _resolved.gcal
-  end
   return _resolved
 end
 

lua/pending/sync/gcal.lua

@@ -23,7 +23,7 @@ local SCOPE = 'https://www.googleapis.com/auth/calendar'
 ---@return table<string, any>
 local function gcal_config()
   local cfg = config.get()
-  return (cfg.sync and cfg.sync.gcal) or cfg.gcal or {}
+  return (cfg.sync and cfg.sync.gcal) or {}
 end
 
 ---@return string