Implement workspace catalog and shard-aware routing and persistence

[brylie]

Problem

Once the shard model is approved, Compendium must replace the current single default content replication unit with the catalog and shard boundaries required for safe multi-space operation.

Scope

• Implement the workspace catalog and its durable persistence according to the approved Specify the workspace catalog and CRDT shard boundary #112 design.
• Implement shard-aware resolution for server routes, services, MCP handlers, WebSocket connections, snapshots, and audit/provenance storage.
• Subscribe browser clients only to the active catalog and explicitly opened content/Collection shards.
• Scope Awareness and active holds to the correct content shard while preserving required workspace-level coordination.
• Implement lazy loading, flushing, safe idle unloading, and documented recovery/compaction behavior.
• Add focused unit and protocol-level tests for routing, persistence-key separation, live UI/MCP parity, and awareness isolation.

Non-goals

• The existing-data migration and full end-to-end cross-space proof, covered by the follow-on migration issue.
• The Space switcher and user-facing multi-space workflow in Multi-space support #6.
• Multi-user authentication or distributed shared synchronization infrastructure.

Dependencies

Blocked by #112. This is an implementation child of #13 and is a prerequisite for the migration/isolation slice and #6.

Done when

Compendium can resolve, load, persist, and synchronize the catalog and each content/Collection shard independently, with no single global content Y.Doc path remaining.

[brylie]

Priority unset → P0: this is the implementation slice that turns #112s approved shard design into the routing and persistence foundation required for safe migration and multi-space delivery. It is blocked by #112 and directly unblocks #114.