feat(web): add floating feedback FAB on homepage linking to Tally form

Collect beta user feedback via Tally.so — fixed-position button in the
bottom-right corner opens the form in a new tab. Ember-orange default,
clay-dark on hover, i18n labels for zh-CN / en / ja.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/i18n/locales/en.ts

@@ -119,6 +119,7 @@ export const en = {
       save: "Save",
       cancel: "Cancel",
       saveAndSelect: "Save and Select",
+      feedback: "Feedback",
     },
 
     styleModal: {

lib/i18n/locales/ja.ts

@@ -130,6 +130,7 @@ export const ja = {
       save: "保存",
       cancel: "キャンセル",
       saveAndSelect: "保存して適用",
+      feedback: "フィードバック",
     },
 
     // Style modal

lib/i18n/locales/zh-CN.ts

@@ -130,6 +130,7 @@ export const zhCN = {
       save: "保存",
       cancel: "取消",
       saveAndSelect: "保存并选用",
+      feedback: "反馈",
     },
 
     // Style modal