[P5][MESH-03] Shared workspaces and enterprise contexts

Programme: #1
Epic: #31

## Objective
Support collaborative workspaces without turning collaboration into accidental union-of-permissions access to every participant's connected services and private context.

## Scope
- Workspace roles and membership lifecycle.
- Recipient-filtered shared state and redacted snapshots.
- Source/account access evaluated per viewer, not inherited from the workspace owner.
- Approval ownership/delegation rules for team operations.
- Team policy overlays and admin constraints while preserving personal/work separation.
- Collaborative annotations/tasks/layouts with conflict-safe sync.
- Shared artifact/evidence export rules and access revocation.
- Audit of who saw/changed/approved shared state.

## Security rules
- Sharing a view never grants the union of collaborators' external-account rights.
- Personal memory/private-source data remains excluded unless explicitly shared and authorized for each recipient.
- Team policy cannot silently expose personal-profile sources.

## Acceptance criteria
- [ ] Two collaborators with different source rights see only records/evidence they individually can access.
- [ ] Shared layout/annotations can collaborate without copying inaccessible source bodies.
- [ ] Approval ownership is explicit and cannot be forged by another role.
- [ ] Revoking membership removes future shared access while preserving required audit history.
- [ ] Work/personal profiles remain isolated under shared-workspace navigation.
- [ ] Redacted exports are tested against index/cache/metadata leakage.

## Dependencies
- MESH-01
- UI-04
- SEC-03

**First phase:** P5
**Maturity target:** P7
**Owner:** platform

Start by reading the MESH-01, UI-04, and SEC-03 dependencies and map their existing workspace, UI, and security constraints to the acceptance criteria. Done requires enforcing per-viewer access, isolated personal/work profiles, explicit approvals, revocation, conflict-safe collaboration, and tests for redacted export leakage.

Written by the indexing model from the issue text.