Add Exodus Migration Workroom bridge

[mdheller]

Implements Phase 2 of SocioProphet/sociosphere#478 for the Prophet Workspace side of the governed Exodus Migration Workroom demo.

Scope:

• add contracts/workspace/exodus-workroom-bridge.schema.json
• add contracts/workspace/exodus-workroom-bridge.v0.1.example.json
• add contracts/workspace/exodus-migration-workroom.v0.1.example.json
• update tools/validate_professional_workrooms.py to validate the bridge
• add docs/exodus-migration-workroom.md

What this proves:

• a Professional Workroom can carry a synthetic Exodus run without forking the workroom model
• Exodus refs can be represented through existing workroom fields and a thin bridge contract
• evidence, office artifacts, provider topology, asset census, scores, blockers, recommendations, and budget proposal refs can be attached to the workroom context

Non-goals:

• no live provider credentials
• no provider API calls
• no provider account writes
• no production migration claim
• no UI readiness claim

Related:

• Exodus Migration Workroom demo v0 sociosphere#478
• Add synthetic Exodus Migration Workroom demo fixture exodus#18