web: shared note actions, reminder chips, page header, formatters and settings seam

From the audit (#5179, web half).

- NoteActions: share, pin, archive and trash (restore and delete forever
  when trashed), as both the card and the editor offer them. The editor's
  history toggle goes in its slot, and it closes on `acted`.
- ReminderActions: the Done / 1h / 1d chips on the card and in the editor,
  which are now the same chips.
- PageHeader: the back-to-board header that Settings, Sync and Linked
  devices each wrote out, now with a `back` icon from the shared set.
- notes/datetime: formatShortDateTime (was formatReminder and the editor's
  revLabel) and formatDateTime (the two `fmt` copies).
- notes/colors: labelDotClasses (the sidebar's and the tag manager's
  labelDot).
- Drawer links use exact-active-class instead of route.name ternaries.
- BoardView binds its three grids from one gridBinds object.
- Settings goes through repo.settings (rest, plus a local adapter that
  answers "needs a server") and shows load failures through AsyncState.

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

frontend/src/components/LabelsModal.vue

@@ -5,6 +5,7 @@ import {
   NOTE_COLOR_KEYS,
   NOTE_COLOR_LABELS,
   NOTE_SWATCH_CLASSES,
+  labelDotClasses,
   resolveLabelColor,
   type NoteColor,
 } from "../notes/colors";
@@ -31,14 +32,6 @@ async function rename(id: string, value: string) {
   if (name) await labels.rename(id, name);
 }
 
-// Shows the colour the tag ACTUALLY wears, derived from its name when nobody has
-// picked one — so this screen agrees with the chips everywhere else. The ring in the
-// swatch grid below follows the same resolution, so opening the picker highlights
-// what you can already see rather than nothing at all.
-function labelDot(label: { name: string; color: string }): string {
-  return NOTE_SWATCH_CLASSES[resolveLabelColor(label)] ?? NOTE_SWATCH_CLASSES.default;
-}
-
 function openColor(id: string) {
   mergeFor.value = null;
   pickerFor.value = pickerFor.value === id ? null : id;
@@ -85,7 +78,7 @@ async function doMerge(sourceId: string, targetId: string) {
             <button
               type="button"
               class="h-4 w-4 shrink-0 rounded-full border border-black/10 transition hover:scale-110 focus:outline-none focus-visible:ring-2 focus-visible:ring-brand dark:border-white/15"
-              :class="labelDot(lb)"
+              :class="labelDotClasses(lb)"
               :title="`Color: ${NOTE_COLOR_LABELS[resolveLabelColor(lb)]}`"
               aria-label="Change tag color"
               @click="openColor(lb.id)"
@@ -150,7 +143,7 @@ async function doMerge(sourceId: string, targetId: string) {
                   >
                     <span
                       class="h-2.5 w-2.5 shrink-0 rounded-full border border-black/10 dark:border-white/15"
-                      :class="labelDot(t)"
+                      :class="labelDotClasses(t)"
                     ></span>
                     <span class="truncate">{{ t.name }}</span>
                   </button>