Fix remaining code-review findings (15 bugs; #11 skipped as AID-compatible)

Backend:
- provider: fall back to parsing a plain JSON body when a server ignores
  stream=true (was: silent empty turn); error if response has no text (#5)
- memorybank: clamp cursors after undo/retry shrinks the action list, and
  translate summary_cursor (list position) to an Action.index boundary
  before comparing with Memory.source_end (#7)
- memorybank: pinned memories now count toward the top_k budget (#8)
- memorybank: cosine() returns 0.0 on dimension mismatch; changing the
  embedding model clears stored vectors so they re-embed (#9)
- scripting: MAX_STORY_CARDS cap now counts cards inserted during the
  hook, so a script can't add unbounded cards in one turn (#10)
- settings: /test tolerates non-dict JSON from /models (#13)
- scenarios: import accepts worldInformation as a story-card source (#14)

Frontend:
- per-key debounce timers in PlotPanel and ScenarioEditor — editing two
  things within 600ms no longer drops the first save (#15, #16)
- Continue button no longer discards typed input (#17)
- failed retry resyncs actions from the server instead of leaving the
  removed action missing (#18)
- Settings save/test surface errors instead of hanging on Testing… (#19)
- InsightsPanel ignores stale responses from superseded requests (#20)
- placeholder scan includes story-card trigger keys (#21)

addStoryCard returning the 0-based index (falsy for the first card) matches
real AI Dungeon per the scripting guidebook — kept, documented (#11).
Statuses updated in CODE_REVIEW_FINDINGS.md; stale entries for previously
fixed items (#1-4, #6, #12) corrected.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KFsGHju9szibJJa2YJcdbg

frontend/src/pages/ScenarioEditor.jsx

@@ -9,7 +9,13 @@ export default function ScenarioEditor() {
   const [scenario, setScenario] = useState(null)
   const [allScripts, setAllScripts] = useState([])
   const [status, setStatus] = useState('')
-  const saveTimer = useRef(null)
+  // One timer per field/card: a single shared timer would cancel the pending
+  // save of whatever was edited previously within the debounce window.
+  const saveTimers = useRef(new Map())
+  const debounceSave = (key, fn) => {
+    clearTimeout(saveTimers.current.get(key))
+    saveTimers.current.set(key, setTimeout(fn, 600))
+  }
 
   useEffect(() => {
     api.getScenario(id).then(setScenario).catch(() => navigate('/scenarios'))
@@ -19,12 +25,11 @@ export default function ScenarioEditor() {
   const setField = (field, value) => {
     const next = { ...scenario, [field]: value }
     setScenario(next)
-    clearTimeout(saveTimer.current)
-    saveTimer.current = setTimeout(async () => {
+    debounceSave(field, async () => {
       await api.updateScenario(id, { [field]: value })
       setStatus('Saved')
       setTimeout(() => setStatus(''), 1500)
-    }, 600)
+    })
   }
 
   const addCard = async () => {
@@ -37,12 +42,11 @@ export default function ScenarioEditor() {
       ...scenario,
       story_cards: scenario.story_cards.map((c) => (c.id === card.id ? card : c)),
     })
-    clearTimeout(saveTimer.current)
-    saveTimer.current = setTimeout(() => {
+    debounceSave(`card-${card.id}`, () => {
       api.updateStoryCard(card.id, {
         name: card.name, type: card.type, keys: card.keys, entry: card.entry, notes: card.notes,
       })
-    }, 600)
+    })
   }
 
   const deleteCard = async (cardId) => {