feat: refactor emoji search with singleton service, Dexie caching, and keyword-enriched search

Replace hand-rolled ~350-entry emoji list with unicode-emoji-json (~1,900 emojis) and emojilib
keywords for richer search matching. Move EmojiSearchService to a singleton with Dexie-backed
caching for instant availability on startup. Add recency+frequency emoji usage tracking shared
across the emoji picker and editor autocomplete.

package-lock.json

@@ -57,6 +57,7 @@
         "date-fns": "^4.1.0",
         "dexie": "^4.2.1",
         "dexie-react-hooks": "^4.2.0",
+        "emojilib": "^4.0.2",
         "flexsearch": "^0.8.212",
         "framer-motion": "^12.23.26",
         "hash-sum": "^2.0.0",
@@ -79,7 +80,8 @@
         "shell-quote": "^1.8.3",
         "shiki": "^3.20.0",
         "sonner": "^2.0.7",
-        "tailwind-merge": "^2.5.5"
+        "tailwind-merge": "^2.5.5",
+        "unicode-emoji-json": "^0.8.0"
       },
       "devDependencies": {
         "@eslint/js": "^9.17.0",
@@ -7596,6 +7598,12 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/emojilib": {
+      "version": "4.0.2",
+      "resolved": "https://registry.npmjs.org/emojilib/-/emojilib-4.0.2.tgz",
+      "integrity": "sha512-8sP3sfAi861cNaFFp7RmyKi4S26K34ZKy4si75ojUW627AIVBHhMSu2SFJo3YRoK66YWnbysIbOk/d48uEqtKQ==",
+      "license": "MIT"
+    },
     "node_modules/enhanced-resolve": {
       "version": "5.18.4",
       "resolved": "https://registry.npmjs.org/enhanced-resolve/-/enhanced-resolve-5.18.4.tgz",
@@ -12406,6 +12414,12 @@
       "integrity": "sha512-Zz+aZWSj8LE6zoxD+xrjh4VfkIG8Ya6LvYkZqtUQGJPZjYl53ypCaUwWqo7eI0x66KBGeRo+mlBEkMSeSZ38Nw==",
       "license": "MIT"
     },
+    "node_modules/unicode-emoji-json": {
+      "version": "0.8.0",
+      "resolved": "https://registry.npmjs.org/unicode-emoji-json/-/unicode-emoji-json-0.8.0.tgz",
+      "integrity": "sha512-3wDXXvp6YGoKGhS2O2H7+V+bYduOBydN1lnI0uVfr1cIdY02uFFiEH1i3kE5CCE4l6UqbLKVmEFW9USxTAMD1g==",
+      "license": "MIT"
+    },
     "node_modules/unified": {
       "version": "11.0.5",
       "resolved": "https://registry.npmjs.org/unified/-/unified-11.0.5.tgz",