Svelte 5 cleanups

These are a long tail of non-blocking problems leftover from migrating to Svelte 5.

- [x] **Breaking**: drawing a freehand line of filters doesn't show the line consistently. It stops after so many points or moving too fast?
- [ ] In edit/NeighbourhoodMode.svelte, don't call `renderNeighbourhood()` twice at startup
- [ ] Reintroduce a `Popup` wrapper that plumbs props succinctly
- [ ] Clean up places with the verbose `$props` interfaces -- inline the declaration or maybe go Vue-style and do `let props: { ... } = $props`
- [ ] Try to fix prettier formatting again (htmlWhitespaceSensitivity) -- see NeighbourhoodBoundarySummary and Modals for bad problems

该 issue 列出了 Svelte 5 迁移需要进行的几项清理任务。首先检查 edit/NeighbourhoodMode.svelte，移除重复的 renderNeighbourhood() 调用。在各个组件中查找冗长的 $props 接口并进行简化。检查 NeighbourhoodBoundarySummary 和 Modals，确认使用 prettier 处理 HTML 空白格式时是否存在问题。每项任务都要求熟悉代码库中的 Svelte 组件和构建设置。

由索引模型根据 Issue 内容生成。