refactor: formatting fixes, config cleanup, health simplification

Problem: Formatter disagreements in `init.lua` and `gtasks.lua`,
stale `calendar` field in gcal config, and redundant health checks
for data directory existence.

Solution: Apply stylua formatting, remove `calendar` field from
`pending.GcalConfig`, drop data-dir and no-file health messages,
add `done`/`pending` to filter tab-completion candidates.

plugin/pending.lua

@@ -181,7 +181,7 @@ end, {
       for word in after_filter:gmatch('%S+') do
         used[word] = true
       end
-      local candidates = { 'clear', 'overdue', 'today', 'priority' }
+      local candidates = { 'clear', 'overdue', 'today', 'priority', 'done', 'pending' }
       local store = require('pending.store')
       local s = store.new(store.resolve_path())
       s:load()