feat: integrate n+1 target highlighting

- Merge feature branch changes for n+1 target-only highlight flow

- Extend merged token model and token-merger to mark exactly-one unknown targets

- Thread n+1 candidate metadata through tokenizer and config systems

- Update subtitle renderer/state to route configured colors and new token class

- Resolve merge conflicts in core service tests, including subtitle and subsync behavior

config.example.jsonc

@@ -79,15 +79,17 @@
       "overwriteImage": true,
       "mediaInsertMode": "append",
       "highlightWord": true,
-      "nPlusOneHighlightEnabled": false,
-      "nPlusOneRefreshMinutes": 1440,
-      "nPlusOne": {
-        "decks": []
-      },
-      "nPlusOneMatchMode": "headword",
       "notificationType": "osd",
       "autoUpdateNewCards": true
     },
+    "nPlusOne": {
+      "highlightEnabled": false,
+      "refreshMinutes": 1440,
+      "matchMode": "headword",
+      "decks": [],
+      "nPlusOne": "#c6a0f6",
+      "knownWord": "#a6da95"
+    },
     "metadata": {
       "pattern": "[SubMiner] %f (%t)"
     },
@@ -153,6 +155,8 @@
     "fontWeight": "normal",
     "fontStyle": "normal",
     "backgroundColor": "rgba(54, 58, 79, 0.5)",
+    "nPlusOneColor": "#c6a0f6",
+    "knownWordColor": "#a6da95",
     "secondary": {
       "fontSize": 24,
       "fontColor": "#ffffff",