fix(goal): never drop an unreadable goal by accident, and let the count be retyped

Review found three ordinary actions that deleted a goal this build could
not read: "It repeats daily", pressing an already-pressed Off, and "not
daily" without saying so. Only "not daily" clears a goal now, and its
warning keys off what is stored, not what parses.

The count field was bound straight to the goal, so emptying it snapped
the old number back and typing appended to it. It now keeps a draft.

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

docs/DATA-MODEL.md

@@ -291,8 +291,10 @@ out is a record marked only with that field, silently dropped on the next write.
 removes an unreadable goal from the record — the likeliest one is a newer shape (weekly tasks add
 `measure: "amount"`) met by an older cached bundle, and dropping it on load would delete it on the
 next write. A goal makes the event a daily regardless of `daily` and detection; setting one clears a
-stored `daily: false`, and any `daily` answer clears the goal, so the two never contradict in
-storage.
+stored `daily: false`, and answering "this isn't a daily event" clears the goal, so the two never
+contradict in storage. No other control removes a goal — not "it repeats daily", and not pressing
+*Off* when no goal is readable — because either could be standing on one this build cannot see. The
+"not daily" control says it removes the goal whenever *anything* is stored there, readable or not.
 
 **`effort` is load-bearing, not decorative.** Combined with the time remaining it answers "can I
 still finish this?" — the same two days is comfortable for a `quick` event and hopeless for a