Add stability warning comment to SCSS source files (#5960)

Adds a stability warning comment to the top of all `src/style.scss`
files in the following Uppy packages to inform consumers that the source
code and variables are not part of the stable API:

- @uppy/audio
- @uppy/core
- @uppy/dashboard
- @uppy/drag-drop
- @uppy/drop-target
- @uppy/image-editor
- @uppy/provider-views
- @uppy/screen-capture
- @uppy/status-bar
- @uppy/url
- @uppy/webcam

The comment added is:
```scss
// NOTE TO CONSUMERS: The code and variables in these source files are not considered stable and can change at any time, even in minor and patch releases!
```

This warning helps clarify that while the compiled CSS output and public
APIs remain stable, the internal SCSS source files, variables, and
implementation details should not be relied upon by consumers as they
may change without notice in any release.

The changes are minimal and surgical - exactly one line added to the top
of each file with no other modifications to existing code.

<!-- START COPILOT CODING AGENT SUFFIX -->

*This pull request was created as a result of the following prompt from
Copilot chat.*
> Add the following comment at the very top of each src/style.scss file
in the following Uppy packages: @uppy/audio, @uppy/core,
@uppy/dashboard, @uppy/drag-drop, @uppy/drop-target, @uppy/image-editor,
@uppy/provider-views, @uppy/screen-capture, @uppy/status-bar, @uppy/url,
@uppy/webcam.
> 
> Comment to add:
> // NOTE TO CONSUMERS: The code and variables in these source files are
not considered stable and can change at any time, even in minor and
patch releases!
> 
> Ensure the comment is the first line in each file, above any existing
code or imports.

<!-- START COPILOT CODING AGENT TIPS -->
---

✨ Let Copilot coding agent [set things up for
you](https://github.com/transloadit/uppy/issues/new?title=✨+Set+up+Copilot+instructions&body=Configure%20instructions%20for%20this%20repository%20as%20documented%20in%20%5BBest%20practices%20for%20Copilot%20coding%20agent%20in%20your%20repository%5D%28https://gh.io/copilot-coding-agent-tips%29%2E%0A%0A%3COnboard%20this%20repo%3E&assignees=copilot)
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---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: mifi <[email protected]>
Co-authored-by: Prakash <[email protected]>
Co-authored-by: Mikael Finstad <[email protected]>

Author: 3 people

packages/@uppy/audio/package.json

@@ -36,6 +36,7 @@
     ".": "./lib/index.js",
     "./css/style.css": "./dist/style.css",
     "./css/style.min.css": "./dist/style.min.css",
+    "./css/style.scss": "./src/style.scss",
     "./package.json": "./package.json"
   },
   "dependencies": {

packages/@uppy/audio/src/style.scss

@@ -1,3 +1,4 @@
+// NOTE TO CONSUMERS: The code and variables in these source files are not considered stable and can change at any time, even in minor and patch releases!
 @use "sass:color";
 @use '@uppy/core/src/_utils.scss' as *;
 @use '@uppy/core/src/_variables.scss' as *;

packages/@uppy/core/package.json

@@ -37,6 +37,7 @@
     ".": "./lib/index.js",
     "./css/style.min.css": "./dist/style.min.css",
     "./css/style.css": "./dist/style.css",
+    "./css/style.scss": "./src/style.scss",
     "./package.json": "./package.json"
   },
   "dependencies": {

packages/@uppy/core/src/style.scss

@@ -1,3 +1,4 @@
+// NOTE TO CONSUMERS: The code and variables in these source files are not considered stable and can change at any time, even in minor and patch releases!
 @use '_variables.scss';
 @use '_utils.scss';
 @use '_common.scss';

packages/@uppy/dashboard/package.json

@@ -40,6 +40,7 @@
     ".": "./lib/index.js",
     "./css/style.css": "./dist/style.css",
     "./css/style.min.css": "./dist/style.min.css",
+    "./css/style.scss": "./src/style.scss",
     "./package.json": "./package.json"
   },
   "dependencies": {

packages/@uppy/dashboard/src/style.scss

@@ -1,3 +1,4 @@
+// NOTE TO CONSUMERS: The code and variables in these source files are not considered stable and can change at any time, even in minor and patch releases!
 @use "sass:color";
 @use '@uppy/core/src/_utils.scss';
 @use '@uppy/core/src/_variables.scss';

packages/@uppy/drag-drop/package.json

@@ -41,6 +41,7 @@
     ".": "./lib/index.js",
     "./css/style.css": "./dist/style.css",
     "./css/style.min.css": "./dist/style.min.css",
+    "./css/style.scss": "./src/style.scss",
     "./package.json": "./package.json"
   },
   "dependencies": {

packages/@uppy/drag-drop/src/style.scss

@@ -1,3 +1,4 @@
+// NOTE TO CONSUMERS: The code and variables in these source files are not considered stable and can change at any time, even in minor and patch releases!
 @use "sass:color";
 @use '@uppy/core/src/_utils.scss';
 @use '@uppy/core/src/_variables.scss';

packages/@uppy/drop-target/package.json

@@ -40,6 +40,7 @@
     ".": "./lib/index.js",
     "./css/style.css": "./dist/style.css",
     "./css/style.min.css": "./dist/style.min.css",
+    "./css/style.scss": "./src/style.scss",
     "./package.json": "./package.json"
   },
   "dependencies": {

packages/@uppy/drop-target/src/style.scss

@@ -1,3 +1,4 @@
+// NOTE TO CONSUMERS: The code and variables in these source files are not considered stable and can change at any time, even in minor and patch releases!
 @use '@uppy/core/src/_variables.scss';
 
 .uppy-is-drag-over::after {