feat(uat-batch-3): wave-1 primitives — DatePicker, DateTimePicker, FileInputButton, ColumnPicker hideAll

Builds the foundational primitives that subsequent waves depend on.
None of these introduce new deps — date-fns, react-day-picker, and
shadcn Calendar were already in the tree.

- `<DatePicker>` and `<DateTimePicker>` in src/components/ui — desktop
  popover wrapping the existing shadcn Calendar (caption-dropdown nav
  so reps can jump months/years for the SkipAheadBanner backfill UX),
  mobile native input via useIsMobile. Drop-in for `<Input type=date>`
  / `<Input type=datetime-local>`.
- `<FileInputButton>` in src/components/ui — styled Button + hidden
  input, replaces browser-default file picker UI. Most queued sweep
  sites already used the hidden-input + Button-trigger pattern; the
  primitive lands for any new caller plus consistent filename display
  + clear button.
- ColumnPicker `hideAll()` footer item — symmetric to existing
  `showAll()`, with the same visibility gate. Lands platform-wide via
  the shared component.
- Migrated highest-leverage call sites to the new primitives:
  * MilestoneAdvanceButton (backfill UX)
  * Reminder form (datetime-local → DateTimePicker)
  * Snooze dialog (datetime-local → DateTimePicker)
  * External-EOI upload dialog (date + file picker)
  * Payments section (received-on date)
- Remaining 15+ date-input call sites parked for a follow-up sweep —
  several use react-hook-form `register` patterns that need careful
  migration to the new controlled-value contract.

tsc clean. 1419/1419 vitest pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/interests/payments-section.tsx

@@ -5,6 +5,7 @@ import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query';
 import { Plus, Trash2, Receipt } from 'lucide-react';
 
 import { Button } from '@/components/ui/button';
+import { DatePicker } from '@/components/ui/date-picker';
 import { Input } from '@/components/ui/input';
 import { Label } from '@/components/ui/label';
 import {
@@ -325,12 +326,12 @@ function RecordPaymentSheet({
 
           <div className="space-y-1.5">
             <Label htmlFor="payment-date">Received on</Label>
-            <Input
+            <DatePicker
               id="payment-date"
-              type="date"
               value={receivedAt}
-              onChange={(e) => setReceivedAt(e.target.value)}
-              required
+              onChange={setReceivedAt}
+              toDate={new Date()}
+              placeholder="Pick a date"
             />
           </div>