ui+server: schedule next-run / last-run on dashboard + schedules tab

P2R-14. New store.LatestJobBySchedule query (per-schedule fired job).
Schedules-tab handler computes next-fire from cron + last-fire from
the jobs table per row. Schedules table grows two columns; dashboard
host row prepends 'next 12h ago/from now' to the existing last-backup
line when a single covering schedule is the run-now candidate.

Embeds store.Schedule into scheduleRow so existing template field
references keep working without bulk renames.

internal/store/schedule_runs.go

@@ -0,0 +1,88 @@
+// schedule_runs.go — derived "next run" / "last run" helpers for the
+// dashboard host row + schedules tab (P2R-14).
+//
+// Both are derived data: NextRun is computed from the cron expression
+// at request time; LatestJobBySchedule reads the most recent job that
+// fired against this schedule. Neither is persisted — the cost of the
+// query is small relative to a page render.
+package store
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+	"time"
+)
+
+// LatestJobBySchedule returns the most recent job fired by this
+// schedule (actor_kind='schedule' AND scheduled_id=schedID), or
+// (nil, ErrNotFound) when the schedule has never fired. Includes
+// queued/running rows because the operator wants to see "running
+// now" too.
+func (s *Store) LatestJobBySchedule(ctx context.Context, hostID, schedID string) (*Job, error) {
+	row := s.db.QueryRowContext(ctx,
+		`SELECT id, host_id, kind, status, scheduled_id, actor_kind, actor_id,
+		        started_at, finished_at, exit_code, stats, error, created_at
+		 FROM jobs
+		 WHERE host_id = ? AND scheduled_id = ? AND actor_kind = 'schedule'
+		 ORDER BY created_at DESC
+		 LIMIT 1`, hostID, schedID)
+	return scanJobRow(row)
+}
+
+// scanJobRow is the shared scan used by LatestJobBySchedule. Mirrors
+// the columns LatestJobByKind reads. Kept in this file (vs jobs.go)
+// to avoid disturbing the stable API surface exported there.
+func scanJobRow(row *sql.Row) (*Job, error) {
+	var (
+		j          Job
+		schedID    sql.NullString
+		actorID    sql.NullString
+		startedAt  sql.NullString
+		finishedAt sql.NullString
+		exitCode   sql.NullInt64
+		stats      sql.NullString
+		errMsg     sql.NullString
+		createdAt  string
+	)
+	if err := row.Scan(&j.ID, &j.HostID, &j.Kind, &j.Status, &schedID,
+		&j.ActorKind, &actorID, &startedAt, &finishedAt,
+		&exitCode, &stats, &errMsg, &createdAt); err != nil {
+		if errors.Is(err, sql.ErrNoRows) {
+			return nil, ErrNotFound
+		}
+		return nil, fmt.Errorf("store: scan job: %w", err)
+	}
+	if schedID.Valid {
+		v := schedID.String
+		j.ScheduledID = &v
+	}
+	if actorID.Valid {
+		v := actorID.String
+		j.ActorID = &v
+	}
+	if startedAt.Valid {
+		t, _ := time.Parse(time.RFC3339Nano, startedAt.String)
+		j.StartedAt = &t
+	}
+	if finishedAt.Valid {
+		t, _ := time.Parse(time.RFC3339Nano, finishedAt.String)
+		j.FinishedAt = &t
+	}
+	if exitCode.Valid {
+		i := int(exitCode.Int64)
+		j.ExitCode = &i
+	}
+	if stats.Valid && stats.String != "" {
+		j.Stats = []byte(stats.String)
+	}
+	if errMsg.Valid {
+		v := errMsg.String
+		j.Error = &v
+	}
+	if t, err := time.Parse(time.RFC3339Nano, createdAt); err == nil {
+		j.CreatedAt = t
+	}
+	return &j, nil
+}