Feature/v2/right rail (#4255)

# Description of Changes

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Please provide a summary of the changes, including:

- What was changed
- Why the change was made
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Closes #(issue_number)
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---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] 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)
- [ ] I have performed a self-review of my own code
- [ ] 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.

---------

Co-authored-by: ConnorYoh <[email protected]>
Co-authored-by: Anthony Stirling <[email protected]>

frontend/src/contexts/RightRailContext.tsx

@@ -0,0 +1,64 @@
+import React, { createContext, useCallback, useContext, useMemo, useState } from 'react';
+import { RightRailAction, RightRailButtonConfig } from '../types/rightRail';
+
+interface RightRailContextValue {
+	buttons: RightRailButtonConfig[];
+	actions: Record<string, RightRailAction>;
+	registerButtons: (buttons: RightRailButtonConfig[]) => void;
+	unregisterButtons: (ids: string[]) => void;
+	setAction: (id: string, action: RightRailAction) => void;
+	clear: () => void;
+}
+
+const RightRailContext = createContext<RightRailContextValue | undefined>(undefined);
+
+export function RightRailProvider({ children }: { children: React.ReactNode }) {
+	const [buttons, setButtons] = useState<RightRailButtonConfig[]>([]);
+	const [actions, setActions] = useState<Record<string, RightRailAction>>({});
+
+	const registerButtons = useCallback((newButtons: RightRailButtonConfig[]) => {
+		setButtons(prev => {
+			const byId = new Map(prev.map(b => [b.id, b] as const));
+			newButtons.forEach(nb => {
+				const existing = byId.get(nb.id) || ({} as RightRailButtonConfig);
+				byId.set(nb.id, { ...existing, ...nb });
+			});
+			const merged = Array.from(byId.values());
+			merged.sort((a, b) => (a.order ?? 0) - (b.order ?? 0) || a.id.localeCompare(b.id));
+			if (process.env.NODE_ENV === 'development') {
+				const ids = newButtons.map(b => b.id);
+				const dupes = ids.filter((id, idx) => ids.indexOf(id) !== idx);
+				if (dupes.length) console.warn('[RightRail] Duplicate ids in registerButtons:', dupes);
+			}
+			return merged;
+		});
+	}, []);
+
+	const unregisterButtons = useCallback((ids: string[]) => {
+		setButtons(prev => prev.filter(b => !ids.includes(b.id)));
+		setActions(prev => Object.fromEntries(Object.entries(prev).filter(([id]) => !ids.includes(id))));
+	}, []);
+
+	const setAction = useCallback((id: string, action: RightRailAction) => {
+		setActions(prev => ({ ...prev, [id]: action }));
+	}, []);
+
+	const clear = useCallback(() => {
+		setButtons([]);
+		setActions({});
+	}, []);
+
+	const value = useMemo<RightRailContextValue>(() => ({ buttons, actions, registerButtons, unregisterButtons, setAction, clear }), [buttons, actions, registerButtons, unregisterButtons, setAction, clear]);
+
+	return (
+		<RightRailContext.Provider value={value}>
+			{children}
+		</RightRailContext.Provider>
+	);
+}
+
+export function useRightRail() {
+	const ctx = useContext(RightRailContext);
+	if (!ctx) throw new Error('useRightRail must be used within RightRailProvider');
+	return ctx;
+}