dashboard: fire-now button on schedule rows (closes #467)

Operator wants to trigger a scheduled prompt immediately
instead of waiting for the next interval. Adds a `↯ fire now`
button on every active schedule row, next to `✕ cancel all`.

Semantics (per design discussion with damocles):

- recurring schedules → out-of-band pulse, `next_fire_at_unix`
  untouched; the regular cadence keeps firing on the original
  schedule. Operator gets an extra fan-out, not a phase shift.
- one-shots → consumed after the manual fire. Operator's
  intent reads as "the scheduled time was wrong, send NOW";
  leaving the original time would be surprising.

Confirm dialog spells out the recurring-vs-one-shot
difference up front so the operator knows what they're about
to do. Button is disabled when every target is already
cancelled (nothing to fire).

Talks to `POST /api/schedules/{id}/fire-now` (damocles is
wiring the backend in parallel). Mauve styling distinguishes
it from cancel (red) and submit (amber); fits the existing
btn pattern.

docs/web-ui.md updated.

docs/web-ui.md

@@ -227,7 +227,10 @@ they share enough conceptual ground to live together).
 **N3W SCH3DUL3 / QU3U3D SCH3DUL3S** — operator-managed
 scheduled prompts (#444 / #459). Lists every schedule with
 its description, targets, body, recurrence interval, next-fire
-time, and per-target last-result. Per-row controls: an
+time, and per-target last-result. Per-row controls: a
+`↯ fire now` button sends an out-of-band manual pulse to
+every active target (#467 — recurring schedules keep their
+cadence; one-shots are consumed after the manual fire), an
 `✎ edit` button opens an inline edit form (#474 — body /
 description / interval / next-fire editable, targets stay
 immutable; submit PATCHes `/api/schedules/{id}`), and a
@@ -500,6 +503,14 @@ not ours.
 - `POST /api/schedules/{id}/cancel` — cancel a schedule. Body
   `{ targets?: ["name", …] }` cancels just those recipients;
   absent or empty body cancels the whole schedule.
+- `POST /api/schedules/{id}/fire-now` — out-of-band manual
+  pulse (#467). Fires the schedule body once immediately to
+  every active target. Recurring schedules: `next_fire_at_unix`
+  is untouched; the regular cadence continues. One-shots: the
+  schedule is consumed (cancelled) after the manual fan-out.
+  Per-target `last_result` is annotated as a manual fire so
+  the audit trail distinguishes scheduled fires from operator-
+  triggered ones.
 - `POST /meta-update` — `nix flake update` the selected
   `meta/flake.lock` inputs, then rebuild the affected agents.
 - `GET /dashboard/stream` — unified live event channel: