Graph node FPS hover tooltip, full names, no native SVG tooltips

Graph editor:
- Floating FPS tooltip on hover over running output_target nodes (300ms delay)
- Shows errors, uptime, and FPS sparkline seeded from server metrics history
- Tooltip positioned below node with fade-in/out animation
- Uses pointerover/pointerout with relatedTarget check to prevent flicker
- Fixed-width tooltip (200px) with monospace values to prevent layout shift
- Node titles show full names (removed truncate), no native SVG <title> tooltips

Documentation:
- Added duration/numeric formatting conventions to contexts/frontend.md
- Added node hover tooltip docs to contexts/graph-editor.md

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/src/wled_controller/static/locales/zh.json

@@ -1656,6 +1656,9 @@
   "graph.help.drag_port_desc": "连接实体",
   "graph.help.right_click": "右键边线",
   "graph.help.right_click_desc": "断开连接",
+  "graph.tooltip.fps": "帧率",
+  "graph.tooltip.errors": "错误",
+  "graph.tooltip.uptime": "运行时间",
   "automation.enabled": "自动化已启用",
   "automation.disabled": "自动化已禁用",
   "scene_preset.activated": "预设已激活",