Add relationship and timeline recall commands

[AlainDor]

Context

Mimir has stable symbols, supersession edges, episodes, captures, and draft lifecycle state, but retrieval is still mostly record/query shaped. Agents benefit from recall that answers what is related, what changed, and when.

Scope

Design and implement first-pass relationship/timeline read commands over existing governed data.

Acceptance Criteria

• Add a relationship-style read surface such as mimir graph neighbors or equivalent MCP read tool.
• Add a timeline surface over episodes, checkpoints, captures, draft lifecycle events, setup changes, and remote sync events where available.
• Outputs preserve data-only boundary markers for agent consumption.
• No opaque graph writes bypass the librarian.

Guardrails

Relationship data may be derived or presented differently, but durable facts and inferred relationships still require governed provenance and validation.