Require two materials for content schedules and scope readiness copy

The engine plans each production piece from a pair of documents, so a
summary, quiz or similar schedule with one material can never plan. Approving
such a plan is now blocked with a note to choose or upload another material,
and the engine's refusal on an existing schedule is explained in plain
language. Video and research schedules still work with one material.

The engine now checks only a schedule's own material before a run, so the
run error and Upload texts no longer say the whole Library or Brain is
checked.

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

src/pages/Schedule.tsx

@@ -8,7 +8,7 @@ import { describeRule } from '../express/parse'
 import { locale, t, type Key } from '../i18n'
 import {
   archiveSchedule, confirmProduction, isRunSchedule, knowledgeReadiness, listRuns, listSchedules, pauseSchedule, PLAN_ACTIVE, productionStatus, quoteProduction, resumeSchedule,
-  planProgress, runNow as startRun, updateTopic, type ContentPlan, type RunSummary, type Schedule,
+  planProgress, productionError, runNow as startRun, updateTopic, type ContentPlan, type RunSummary, type Schedule,
 } from '../express/schedules'
 
 const STUDIO_URL: string = import.meta.env.VITE_STUDIO_URL
@@ -201,7 +201,7 @@ function ProducePanel({ schedule: { agent, rule }, onClose }: { schedule: Schedu
           <input type="number" min={1} max={remaining} value={n} onChange={e => setCount(Number(e.target.value) || 1)} />
         </label>
       )}
-      {error && <span className="error">{error.message}</span>}
+      {error && <span className="error">{productionError(error.message)}</span>}
       <div className="produce-actions">
         {!running && remaining > 0 && (quote.data
           ? <button className="btn small primary" disabled={start.isPending} onClick={() => start.mutate(quote.data)}>{start.isPending ? t('sch.starting') : t('sch.startProduction')}</button>