[Feature Request]: Schema Designer Synchronization State

@yoleichen is already working on this.

Since Apr 23, 2026.

### Feature Description

Add a clear synchronization state indicator to Schema Designer so users always know whether the database is currently aligned with what they see/edit in the designer (canvas) and Copilot/chat-driven changes. This is intended as a “mental reminder” to prevent users from closing Schema Designer assuming changes were applied to the database when they were not.

There are three states in total:
- Synchronized: The Schema Designer view matches the database schema; no pending/unapplied changes exist.
- Proposed changes: There are edits made in the designer UI and/or through Copilot/chat that are not yet applied to the database.
- Out of Sync: The database schema has changed externally (or the designer’s baseline no longer matches), so the designer state cannot be confidently treated as aligned with the DB. (more details in https://github.com/microsoft/vscode-mssql/issues/21435)

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### Problem and Motivation

We observed users who:
- Open Schema Designer (initially everything is in sync),
- Make changes in the Schema Designer UI and/or via GitHub Copilot (chat),
- Close Schema Designer
- Later realize the database was never updated and is now inconsistent with their intended design.

Today, Schema Designer does not sufficiently communicate “where you are” in the workflow (viewing current DB schema vs. drafting changes that still need to be applied).

### Related Area

- [ ] Connection dialog (SQL Server | Azure browse/Fabric browse)
- [ ] Query editor
- [ ] Query results panel
- [ ] Object Explorer
- [ ] GitHub Copilot integration
- [ ] Preview/Edit data
- [ ] Table Designer
- [x] Schema Designer
- [ ] Schema Compare
- [ ] Local SQL Server Container provisioning
- [ ] SQL database in Fabric provisioning
- [ ] DACPAC/BACPAC export/import
- [ ] SQL Database projects
- [ ] Query Plan Visualizer
- [ ] Other (please describe below)

### If you selected "Other", please describe the area

_No response_

### Confirmation

- [x] I have searched existing feature requests and couldn't find a match
- [ ] I want to help implement this feature