dashboard: inline edit form on schedule rows (closes #474)

Per damocles's PATCH /api/schedules/{id} backend (#475), each
non-cancelled schedule row gets a `✎ edit` button that toggles
an inline form pre-filled with current values. Editable:

- body (textarea)
- description (blank to clear)
- next-fire (datetime-local)
- interval (shared composer from #466 — all-zero flips to one-shot)

Targets stay immutable per the design call with damocles:
per-target last-result history is keyed on them; cancel + new
schedule is the documented retarget workaround. The form
surfaces the active target list as a read-only note explaining
this.

Submit semantics — the form computes a PATCH diff against the
original schedule and only includes keys for fields that
actually changed. Blank description → `null` (clear), all-zero
interval on a recurring schedule → `null` (flip to one-shot).
No-op submit (no fields changed) just closes the edit form.

Refactored the interval composer (#466) into a shared
`buildIntervalComposer({ label, namePrefix, initialSeconds })`
helper so the new-schedule and edit-schedule forms use the same
chip/d/h/m/s/preview widget. New-schedule form behavior
unchanged; edit-form input names are prefixed `edit_interval_`
to avoid FormData collisions when both happen to mount.

State survives state-poll re-renders via `editingSchedules`
(Set of ids being edited) + `scheduleEditCarry` (per-id
mid-edit values) — same pattern the new-schedule form uses
with `readScheduleFormCarry`.

docs/web-ui.md

@@ -227,10 +227,14 @@ 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; a `CANC3L` button cancels
-the whole schedule (`POST /api/schedules/{id}/cancel`), and
-individual target chips have their own cancel links. An inline
-creation form lets the operator queue a new schedule directly:
+time, and per-target last-result. Per-row controls: 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
+`CANC3L` button cancels the whole schedule
+(`POST /api/schedules/{id}/cancel`). Individual target chips
+have their own cancel links. An inline creation form lets
+the operator queue a new schedule directly:
 targets (multi-select checkboxes drawn from live container
 names + `operator` + `manager`), prompt body (textarea),
 first-fire datetime-local (pre-filled to 5 minutes from now),
@@ -485,6 +489,14 @@ not ours.
   `{ targets, body, first_fire_at_unix, interval_seconds?, description? }`.
   Agent-initiated schedules go through the approval queue instead
   (manager MCP `request_schedule_prompt`).
+- `PATCH /api/schedules/{id}` — partial edit (#474). JSON body
+  `{ body?, description?, interval_seconds?, next_fire_at_unix? }`.
+  Missing key = "leave alone"; explicit `null` on
+  `description` / `interval_seconds` clears the field (so a
+  recurring schedule flips to one-shot when `interval_seconds`
+  is sent as `null`). Targets stay immutable — cancel + new
+  schedule is the retarget workaround. Refuses cancelled rows;
+  returns the updated `WireSchedule` on success.
 - `POST /api/schedules/{id}/cancel` — cancel a schedule. Body
   `{ targets?: ["name", …] }` cancels just those recipients;
   absent or empty body cancels the whole schedule.