fix(tasks): keep a task whole through import and edit, and fix two counts

Review found that import and edit rebuilt a task from this build's parse.
That stripped any field it didn't know, and import dropped a newer
version's task entirely. Both now keep the record as stored and validate
only to display it.

An event whose goal is points can't be ticked, so it no longer counts as
waiting today: it counts with its week. The month-day field reset
itself to 1 when emptied; it now keeps a draft.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/DATA-MODEL.md

@@ -634,7 +634,9 @@ timestamps keeps the merge order-independent and idempotent either way, and remo
 `mergeProgress` is pure and `test/progress.test.ts` pins it. Check-in goals ride `progress`, so they need no export key of their own
 and merge with the record they belong to. `tasks` and `amounts` are additive export keys like
 `customGames`: a file without them is from a device that had none. Tasks merge by id with the later
-`updatedAt` winning (`mergeTasks`), incoming records validated and current ones kept as stored;
+`updatedAt` winning (`mergeTasks`); an incoming record is let in on its identity alone (a `mytask:`
+id and an `updatedAt`) and stored exactly as it came, so a newer version's task — or a field this
+build does not know — survives a trip through an older build, and an edit keeps such fields too;
 amounts merge per item **and per period** with the later `at` winning (`mergeAmounts`), so restoring
 an old backup cannot roll this week's number back, and a week only one side has survives. An export written before daily checklists existed
 simply has no `daily` key, which is not an error. Losing a user's marks to a bad import is unrecoverable, so the merge is