feat(ui): redesign image generator floating composer and settings panel

Compact the floating composer with an auto-resizing prompt editor and a
scrollable settings popover, add a titled settings panel, and show the
resolved image size in the settings summary. Add the imageCountLabel
string for the count section.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/i18n/locales/en-US.json

@@ -242,6 +242,7 @@
   "referenceImage": "Reference",
   "imageSettings": "Image settings",
   "imageCountUnit": "{count} img",
+  "imageCountLabel": "Image",
   "quality": "Quality",
   "qualityAuto": "Auto",
   "qualityHigh": "High",

frontend/src/i18n/locales/zh-CN.json

@@ -242,6 +242,7 @@
   "referenceImage": "参考图",
   "imageSettings": "图片参数",
   "imageCountUnit": "{count} 张",
+  "imageCountLabel": "生成数量",
   "quality": "质量",
   "qualityAuto": "自动",
   "qualityHigh": "高",