[FEATURE]: Configurable participant permissions: Sign, Authorize, or Observe roles

Is your feature request related to a problem? Please describe.

No response

Describe the solution you'd like

Implement a flexible permission system that allows document creators to define participant roles with minimum permissions levels: "Sign," "Authorize," or "Observe."
Problem Statement
Current permission models may not adequately address different participation levels in document workflows. Not all participants need signing authority - some may only need to authorize/approve, while others should only observe the process without taking action.
Proposed Solution
Create a role-based permission system where document creators can assign participants to one of three permission levels:
Permission Levels

Sign (highest permission)

Full signing authority
Can add legally binding signatures to the document
Includes all permissions from lower levels

Authorize (medium permission)

Can approve or reject the document
Cannot add legal signatures
Can add comments/notes
Includes observation permissions

Observe (lowest permission)

Read-only access to the document
Can view document status and history
Receives notifications about document progress
Cannot modify, sign, or authorize

Expected Benefits

Flexibility: Better alignment with real-world workflows and organizational hierarchies
Security: Clear separation of responsibilities and access control
Compliance: Improved audit trails with defined roles
Clarity: Participants understand exactly what's expected of them

Suggested Implementation Details

Database schema for role/permission definitions
UI for assigning roles when adding participants
Permission validation on all document operations
Visual indicators showing participant roles in the UI
API endpoints for role management
Audit log entries for permission-based actions
Email notifications customized by role
Documentation for each permission level

Use Cases

Legal documents: Lawyer signs, client authorizes, witnesses observe
Corporate approvals: Manager authorizes, Legal signs, team observes
Multi-level reviews: Different departments observe/authorize before final signature
Training/onboarding: New employees observe processes before gaining signing authority

Additional Considerations

Should there be a way to escalate permissions (e.g., Observer → Authorizer)?
Should certain roles be mutually exclusive per participant?
How should the system handle documents requiring multiple authorizers before signing?
Should there be configurable workflows (e.g., must authorize before signing)?

Describe alternatives you've considered

No response

Additional context

No response

The issue names database schema, participant-assignment UI, API endpoints, permission validation, audit logs, notifications, and documentation, but no files, tests, or entry points. Start by mapping these areas and resolving the open workflow questions before implementation. Done would require coordinated role behavior across storage, UI, operations, auditing, notifications, and documentation.