[Today] TomorrowNote is stored/fetched same-day - the 'tomorrow' hand-off its UI copy and controller doc promise never happens; OAuthAuthCode.UserId summary contradicts CreateForLinking

[Chris0Jeky]

Found during the PR #1629 DATA_MODEL.md recertification (round-2 review). Two related defects on the TomorrowNote / OAuthAuthCode surface; both are code-vs-contract mismatches, not just doc drift.

1. TomorrowNote "tomorrow" feature never shows a note to the tomorrow-self

Traced end to end at #1629's head:

• Save key: formatLocalDossierDate(dossier.value.date) (PaperTodayView.vue:50 → :save-date → TodayLineForTomorrow.vue:72).
• Read key: todayApi.getTomorrowNote(formatLocalDossierDate(now.value)) (useTodayDossier.ts:374,381).
• Neither TomorrowNoteService nor TodayController applies AddDays(1).

So a note written on day X is stored under key X and fetched on day X; at rollover useTodayDossier.ts:408 clears the field and day X+1 queries key X+1 → 204. The note is never surfaced to the "tomorrow" self, contradicting both the UI copy and TodayController.GetTomorrowNote's XML doc, which promise an X→X+1 hand-off.

Decide the intended contract: either make save/read do the one-day shift (feature as advertised), or relabel it a same-day scratch note and fix the UI copy + controller doc. DATA_MODEL.md now documents the shipped same-day behavior with the intent gap noted.

2. OAuthAuthCode.UserId XML summary contradicts CreateForLinking

OAuthAuthCode.UserId's XML summary says the value may be Guid.Empty for the link flow, but CreateForLinking (OAuthAuthCode.cs:100-101) rejects Guid.Empty. Reword the summary to match (both flows require a non-empty user id — the binding is load-bearing, enforced at AuthController.cs:437).

Refs PR #1629, #1470.