[TASK][CORE-01.T03] Specify durable core record schemas

Parent: #2

Task ID: `CORE-01.T03`

## Proposed implementation
Write v1 records for GoalContract, Workspace, Task, Capability, Observation, Evidence, ActionProposal, Approval, Operation, Receipt, ViewDefinition and MemoryRecord. Keep provider sessions secondary and source observations distinct from model-derived facts.

## Done when
Schemas round-trip fixtures with missing optional fields, distinct account scopes and unresolved external outcomes.

## Guardrail
Use explicit unknown/unsupported states; reject records that cannot preserve authority-relevant meaning.

## Prerequisites
`CORE-01.T02`

Review: pending · Implementation: not started.

No files or tests are named. Start with prerequisite CORE-01.T02 and the proposed record list; inspect how fixtures represent missing optional fields, account scopes, and unresolved external outcomes. Done means v1 schemas round-trip those fixtures while preserving explicit unknown or unsupported states and authority-relevant meaning.

Written by the indexing model from the issue text.