Feat:Implement lightweight collaboration session (Phase 1)

[Gautam-Bharadwaj]

** Overview**

This PR implements Phase 1 of the "Collaboration Session" feature as discussed in issue #813. It introduces a manual "Push/Pull" synchronization mechanism, allowing multiple users to collaborate on the same diagram via a shared session ID without the complexity of real-time CRDTs or WebSockets.

** Motivation**

Currently, users are required to manually export and import JSON files to collaborate with others. This manual session-based sync provides a significant UX improvement by allowing teams to quickly push their changes to a cloud store and pull updates from their collaborators with a single click.

** Key Features**

• Session Management: Users can "Create" a new session which generates a unique ID and a shareable link.
• Manual Sync:
  • Push My Changes: Overwrites the cloud-hosted diagram with the local diagram state.
  • Pull Latest: Fetches the remote diagram and hydrates the current workspace (includes a confirmation prompt to prevent data loss).
• Deep Linking: Shared links (e.g., ?session=<ID>) automatically fetch and load the diagram on application startup.
• Responsive UI: Integrated a "Collab" dashboard into the editor header using the Semi-UI design system.

** Technical Implementation**

1. Sync Engine (src/api/collaboration.js): A lightweight API service that interacts with a JSON blob store for persistence.
2. Collaboration Modal: A new component (Collaboration.jsx) that manages UI states for session creation, joining, and syncing.
3. Workspace Hydration: Updated Workspace.jsx to support deep-linking via query parameters, bypasses local storage when a session is active.
4. State Integration: Tight integration with DiagramContext ensures that syncing updates tables, relationships, notes, and areas in one atomic operation.

** Steps to Test**

1. Open the editor and click the "Collab" button in the header.
2. Click "Create Session" to generate a session link.
3. Open the link in a separate tab or browser.
4. Edit in Window A: Move a table or add a note, then click "Push My Changes".
5. Update in Window B: Click "Pull Latest". Confirm the prompt.
6. The diagram in Window B should now match Window A.

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Fixes #813

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