fix: say what carry-over did, and stop the day control being a riddle

Two pieces of copy that were making the app harder to read than it needs
to be.

Carry-over happened in total silence. Open the app after a weekend and
unfamiliar tasks were sitting in Today with nothing explaining where they
came from, which reads as a bug rather than the feature it is. A line now
says how many were brought forward, on the day it happened, and it can be
dismissed.

The day control was a single button labelled with the day you were already
on, which then took you somewhere else. Clicking it was the only way to
find out what it did, and the date underneath already said where you were.
It is two options now with the current one marked, so the control states
both where you are and what the alternative is without being touched.

Also drops labelFor from dates.js along with its tests. It existed to
label that one button and nothing uses it now.

src/lib/dates.js

@@ -28,12 +28,6 @@ export function isKey(value) {
   return KEY_PATTERN.test(value)
 }
 
-export function labelFor(dateKey, todayKey) {
-  if (dateKey === todayKey) return 'Today'
-  if (dateKey === toKey(addDays(fromKey(todayKey), 1))) return 'Tomorrow'
-  return fromKey(dateKey).toLocaleDateString('en-US', { month: 'short', day: 'numeric' })
-}
-
 export function formatLong(dateKey) {
   return fromKey(dateKey).toLocaleDateString('en-US', {
     weekday: 'long',

src/lib/dates.test.js

@@ -1,5 +1,5 @@
 import { describe, it, expect } from 'vitest'
-import { toKey, fromKey, addDays, isKey, labelFor, formatLong } from './dates.js'
+import { toKey, fromKey, addDays, isKey, formatLong } from './dates.js'
 
 describe('toKey', () => {
   it('formats a date as local YYYY-MM-DD', () => {
@@ -60,28 +60,6 @@ describe('isKey', () => {
   })
 })
 
-describe('labelFor', () => {
-  it('labels today', () => {
-    expect(labelFor('2026-08-15', '2026-08-15')).toBe('Today')
-  })
-
-  it('labels tomorrow', () => {
-    expect(labelFor('2026-08-16', '2026-08-15')).toBe('Tomorrow')
-  })
-
-  it('labels tomorrow across a month boundary', () => {
-    expect(labelFor('2026-09-01', '2026-08-31')).toBe('Tomorrow')
-  })
-
-  it('labels tomorrow across a year boundary', () => {
-    expect(labelFor('2027-01-01', '2026-12-31')).toBe('Tomorrow')
-  })
-
-  it('falls back to a short date for other days', () => {
-    expect(labelFor('2026-08-20', '2026-08-15')).toBe('Aug 20')
-  })
-})
-
 describe('formatLong', () => {
   it('renders the long-form date used in the header', () => {
     expect(formatLong('2026-08-15')).toBe('Saturday, August 15, 2026')