Persist workspace creation and list workspaces

[VexCode24]

Description

This PR wires the existing workspace UI into the database-backed organization models so newly created workspaces are persisted and shown in the mail workspace sidebar.

It adds an authenticated /api/workspaces route for listing the current user's workspaces and creating a new OWNER membership, then updates the Create Workspace dialog to POST real workspace data and refresh the sidebar.

What type of PR is this? (check all applicable)

• Feature
• Bug Fix
• Documentation Update
• Style
• Code Refactor
• Performance Improvements
• Test
• Build
• CI
• Chore (Release)
• Revert

Related Tickets & Documents

Refs #1

Mobile & Desktop Screenshots/Recordings

No screenshots; backend/API wiring plus existing sidebar/dialog behavior.

Steps to QA

1. Sign in and open the mail app.
2. Click the plus button in the workspace sidebar.
3. Enter a workspace name and create it.
4. Confirm the workspace persists through /api/workspaces and appears in the sidebar.

Added to documentation?

• README.md
• no documentation needed

[optional] Are there any post-deployment tasks we need to perform?

None.

[optional] What gif best describes this PR or how it makes you feel?

A small but real first brick for teams/workspaces support.

[VexCode24]

Update after the latest commits: this now covers the full workspace/team slice from #1 more completely.

Implemented pieces:

• persisted workspace creation/listing through /api/workspaces
• multiple Gmail/Google Workspace email accounts at creation time
• multiple invited members at creation time, with USER/ADMIN role selection
• member listing and invite APIs
• owner-only non-owner role updates and member removal APIs
• owner/admin email-account management APIs
• workspace management UI for email accounts and team members after creation

Local verification available in this checkout was limited to source inspection plus git diff checks because the project package tooling is not installed here, but the branch is pushed and ready for Vercel/reviewer feedback.