feat(ui): a note's check is editable, dated and sweepable (#3167, milestone 317 step 4)

Rule 27: no UI, no ship. Three surfaces.

THE EDITOR ASKS, but only where the answer can be saved: the fields appear
for a plain note and not for a task or a snippet, matching the service gate
from step 2 so the form never offers a write the save would reject. The
labels are phrased as the QUESTION rather than the field name — "how would
someone check this is still true?" and, underneath, "could this become false
without anyone editing it?". "Verify with" gets filled in on every note; the
question gets filled in on the few that can go stale. `expires_when` appears
only once a check exists, and asks for a state rather than a date in the
placeholder itself.

THE NOTE SHOWS ITS AGE beside the field — "checked 2026-08-28" or "never
checked", italic, and nothing at all when no check exists. No red/amber ramp,
matching RuleSweepPane: a colour scale would restate the sweep's ordering and
force an invented staleness threshold. "Never" is marked because it is
categorically different from a date, not a worse one.

THE SWEEP is a pane in the Knowledge view, not beside the rules sweep —
operator's call, taken over a unified "everything due" surface and over a
second pane under /rules. Notes stay where notes live. The cost, accepted
knowingly: no single screen shows every unconfirmed record. It REPLACES the
feed rather than filtering it, because a facet answers "show me this kind"
and this answers "show me what nobody has confirmed" — a question the type
chips cannot narrow without under-reporting.

Two REST routes for it, since step 3 built only the service and the MCP door.

Along the way: NoteEditorView spelled its write payload out at three call
sites (save, create, auto-save), so every new field had to be added three
times — which is how one of them ends up not carrying it. Now one `payload()`
and one `snapshot()`.

Known and filed, not fixed: NoteSweepPane copies ~12 scoped CSS rules from
RuleSweepPane (#3207). The clean extraction needs prefixed names, because
`.age`, `.row-title`, `.lede` and `.actions` all exist scoped in other
components and an unscoped global would leak into them — which means editing
the shipped rules sweep, blind, inside a step whose acceptance is the
operator looking at a different surface.

frontend/src/types/note.ts

@@ -34,6 +34,15 @@ export interface Note {
   is_task: boolean;
   note_type: NoteType;
   task_kind?: TaskKind;
+  // The note's own check (milestone 317). Empty on almost every note — that
+  // is the normal case: a note with no `verify_with` is a DECISION, and there
+  // is nothing to go and check. Only a note asserting a fact about something
+  // outside the operator's control carries one. `verified_at` null while
+  // `verify_with` is set means NOBODY HAS EVER CONFIRMED IT, which is the
+  // state the sweep ranks first.
+  verify_with?: string;
+  expires_when?: string;
+  verified_at?: string | null;
   systems?: System[];
   arose_from_id?: number | null;
   created_at: string;