Add spell practice, memory analytics, auth persistence, and word library UX.

Includes per-word training stats and curves, quiz session auto-save, remember-login,
paginated word list with floating page arrows, and Obsidian-style relationship graph baseline.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/package-lock.json

@@ -9,6 +9,7 @@
       "version": "1.0.0",
       "dependencies": {
         "axios": "^1.7.9",
+        "echarts": "^6.1.0",
         "vue": "^3.5.13",
         "vue-router": "^4.5.0"
       },
@@ -1226,6 +1227,16 @@
         "node": ">= 0.4"
       }
     },
+    "node_modules/echarts": {
+      "version": "6.1.0",
+      "resolved": "https://registry.npmjs.org/echarts/-/echarts-6.1.0.tgz",
+      "integrity": "sha512-q0yaFPggC9FUdsWH4blavRWFmxdrIodbkoKNAjJudAI6CA9gNPxHtV2RcZNEepZVlk4yvBYkOkbk6HIVpIyHZA==",
+      "license": "Apache-2.0",
+      "dependencies": {
+        "tslib": "2.3.0",
+        "zrender": "6.1.0"
+      }
+    },
     "node_modules/entities": {
       "version": "7.0.1",
       "resolved": "https://registry.npmjs.org/entities/-/entities-7.0.1.tgz",
@@ -1740,6 +1751,12 @@
         "url": "https://github.com/sponsors/SuperchupuDev"
       }
     },
+    "node_modules/tslib": {
+      "version": "2.3.0",
+      "resolved": "https://registry.npmjs.org/tslib/-/tslib-2.3.0.tgz",
+      "integrity": "sha512-N82ooyxVNm6h1riLCoyS9e3fuJ3AMG2zIZs2Gd1ATcSFjSA23Q0fzjjZeh0jbJvWVDZ0cJT8yaNNaaXHzueNjg==",
+      "license": "0BSD"
+    },
     "node_modules/typescript": {
       "version": "5.6.3",
       "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.6.3.tgz",
@@ -1888,6 +1905,15 @@
       "peerDependencies": {
         "typescript": ">=5.0.0"
       }
+    },
+    "node_modules/zrender": {
+      "version": "6.1.0",
+      "resolved": "https://registry.npmjs.org/zrender/-/zrender-6.1.0.tgz",
+      "integrity": "sha512-oEGMDB6pOP2S6OwRR4PdVv610zrjnA3Bh+JnSG12fYJlBKjtNAoEb5fSUoCOOINlH96I2fU38/A2UpRKs67xYQ==",
+      "license": "BSD-3-Clause",
+      "dependencies": {
+        "tslib": "2.3.0"
+      }
     }
   }
 }