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- InsightsPanel ignores stale responses from superseded requests (#20)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

backend/app/scripting/engine.py

@@ -31,6 +31,8 @@ function log(msg) {
 }
 var console = { log: log };
 
+// Returns the new card's index, or false if a card with those keys exists —
+// matching real AI Dungeon. Note index 0 is falsy; that quirk is upstream's.
 function addStoryCard(keys, entry, type) {
   for (var i = 0; i < storyCards.length; i++) {
     if (storyCards[i].keys === keys) return false;

backend/app/scripting/pipeline.py

@@ -45,6 +45,7 @@ class ScriptPipeline:
     def _apply_cards(self, returned: list) -> None:
         existing = {c.id: c for c in self.adventure.story_cards}
         seen_ids = set()
+        added = 0
         for item in returned:
             if not isinstance(item, dict):
                 continue
@@ -56,13 +57,14 @@ class ScriptPipeline:
                 seen_ids.add(card_id)
                 card = existing[card_id]
                 card.keys, card.entry, card.type = keys, entry, card_type
-            elif len(existing) + len(seen_ids) < MAX_STORY_CARDS:
+            elif len(existing) + added < MAX_STORY_CARDS:
                 self.db.add(
                     models.StoryCard(
                         adventure_id=self.adventure.id,
                         keys=keys, entry=entry, type=card_type,
                     )
                 )
+                added += 1
         for card_id, card in existing.items():
             if card_id not in seen_ids:
                 self.db.delete(card)