Keep hosted channels available when their workspace is offline #179

Let a hosted channel remain discoverable and manageable when its workspace is disconnected. Today hosted routing/listing is coupled to its workspace host's catalog and directory snapshot even though durable channel state lives in the cell.

Acceptance

• Define ownership of the hosted channel's durable identity/location and directory listing separately from the workspace's connection. The directory lists locations and metadata, not channel content; pi owns durable channel state.
• A workspace going offline does not make a healthy hosted cell disappear or falsely classify its transcript as offline. Surface cell reachability and workspace availability distinctly to clients.
• Open/read and permitted human chat operations route to the hosted cell while the workspace is unavailable. Tool requests have explicit unavailable/interrupted outcomes; reconnect restores supported tool operation without duplicating execution.
• Keep name, summary, archived state, owner and location consistent through cell/workspace/client restarts. Define and exercise archive, resume, Kill and Delete when the workspace is absent, including necessary deferred lane cleanup and the preservation guarantees on failure.
• Preserve the existing ownership/collaborator policy across routes. Directory publication must not let a disconnected/reconnecting workspace overwrite a newer authoritative channel location or revive a deleted channel.
• Verify with a deployed cell and clients on two actual machines: stop the workspace, continue permitted channel interaction, reconnect it, restart the cell, and confirm history and lifecycle state remain consistent.

This work separates hosted-channel availability from local tool execution; it does not move execution to the cloud. Keep packages/channel runtime-neutral and use shared protocol types. Any durable format change needs a versioned migration and existing-channel backup validation.

Priority 4 under #13; use #176's observed routing/lifecycle failures as evidence. Directory push latency #14, project lobbies #17, execution-host handoff #49, cross-gateway terminals #11 and direct browser access without a gateway remain separate scopes.