fix: address trivial CodeRabbit issues (#9196)

## Summary

Address several trivial CodeRabbit-filed issues: type guard extraction,
ESLint globals, curve editor optimizations, and type relocation.

## Changes

- **What**: Extract `isSingleImage()` type guard in WidgetImageCompare;
add `__DISTRIBUTION__`/`__IS_NIGHTLY__` to ESLint globals and remove
stale disable comments; remove unnecessary `toFixed(4)` from curve path
generation; optimize `histogramToPath` with array join; move
`CurvePoint` type to curve domain

- Fixes #9175
- Fixes #8281
- Fixes #9116
- Fixes #9145
- Fixes #9147

## Review Focus

All changes are mechanical/trivial. Curve path output changes from
fixed-precision to raw floats — SVG handles both fine.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9196-fix-address-trivial-CodeRabbit-issues-3126d73d365081f19a5ce20305403098)
by [Unito](https://www.unito.io)

src/App.vue

@@ -51,7 +51,6 @@ onMounted(() => {
   // See: https://vite.dev/guide/build#load-error-handling
   window.addEventListener('vite:preloadError', (event) => {
     event.preventDefault()
-    // eslint-disable-next-line no-undef
     if (__DISTRIBUTION__ === 'cloud') {
       captureException(event.payload, {
         tags: { error_type: 'vite_preload_error' }