Chore/v2/right rail cleanup (#4689)

# Description of Changes

- Migrated all dynamic right-rail controls into their owning views (file
editor, page editor, viewer) using dedicated helper hooks, so the rail
is
    purely a renderer now.
- Tightened layout/animation: dynamic buttons grow in with a top-down
reveal
    and center correctly.

---

## Checklist

### General

- [x] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [x] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [x] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [x] I have performed a self-review of my own code
- [x] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

frontend/src/styles/theme.css

@@ -171,7 +171,7 @@
 
   /* RightRail (light) */
   --right-rail-bg: #F5F6F8;           /* light background */
-  --right-rail-foreground: #CDD4E1;   /* panel behind custom tool icons */
+  --right-rail-foreground: #E3E4E5;   /* panel behind custom tool icons */
   --right-rail-icon: #4B5563;         /* icon color */
   --right-rail-icon-disabled: #CECECE;/* disabled icon */