Add FireflyGo sync mode, extra_data controls and Enka import

- js/modes.js: per-backend capability matrix (GaCy GO / FireflyGo / RobinSR)
- js/firefly.js: POST /sync payload builder + extra_data normaliser
- js/enka-import.js: enka.network -> FreeSR converter with merge/replace
- app.js: mode-aware UI, firefly transport, Enka import, extra_data form
- index.html: enable FireflyGo, add Enka import + FireflyGo controls cards
- i18n: Thai/English strings for every new label, message and error
- vercel.json: /api/enka/:uid rewrite; scripts/dev-server.cjs for local dev

js/modes.js

@@ -0,0 +1,74 @@
+// Server-mode capability matrix.
+//
+// GaCy GO is the only backend that implements the full tool API
+// (/api/status, /api/persistent, /api/inventory, /api/monster-settings,
+// /api/battle_report, /api/tool-session ...). FireflyGo is push-only and only
+// understands POST /sync, so every feature that needs a read endpoint has to
+// disappear from the UI instead of failing at runtime.
+
+export const SERVER_MODES = ['gac', 'firefly', 'robin'];
+
+export const MODE_LABELS = {
+  gac: 'GaCy GO',
+  firefly: 'FireflyGo',
+  robin: 'RobinSR'
+};
+
+export const MODE_CAPABILITIES = {
+  gac: {
+    saveManager: true,
+    exranks: true,
+    inventory: true,
+    monsterSettings: true,
+    damageAnalyst: true,
+    sceneCard: true,
+    gmConsole: true,
+    battleSummary: true,
+    toolSession: true,
+    extraData: false,
+    ownedAvatarsOnly: false,
+    // data-in-game.json is a FireflyGo artifact, so GaCy keeps only its own
+    // freesr/persistent documents visible in the JSON tab.
+    jsonModes: ['freesr', 'persistent']
+  },
+  firefly: {
+    saveManager: false,
+    exranks: false,
+    inventory: false,
+    monsterSettings: false,
+    damageAnalyst: false,
+    sceneCard: false,
+    gmConsole: false,
+    battleSummary: false,
+    toolSession: false,
+    extraData: true,
+    ownedAvatarsOnly: true,
+    jsonModes: ['freesr']
+  },
+  robin: {
+    saveManager: false,
+    exranks: false,
+    inventory: false,
+    monsterSettings: false,
+    damageAnalyst: false,
+    sceneCard: false,
+    gmConsole: false,
+    battleSummary: false,
+    toolSession: false,
+    extraData: false,
+    ownedAvatarsOnly: false,
+    jsonModes: ['freesr']
+  }
+};
+
+export function normalizeMode(mode) {
+  return MODE_CAPABILITIES[mode] ? mode : 'gac';
+}
+
+export function modeCapabilities(mode) {
+  return MODE_CAPABILITIES[normalizeMode(mode)];
+}
+
+export function modeSupports(feature, mode) {
+  return modeCapabilities(mode)[feature] === true;
+}