feat(workspace): add workspace resource model with scoping, membershi…

[derekwaynecarr]

Summary

Implements Phase 1 of RFC 0011 — the workspace and membership model that provides hard isolation boundaries for multi-player OpenShell deployments.

• Workspace resource: CRUD RPCs (CreateWorkspace, GetWorkspace, ListWorkspaces, DeleteWorkspace) with a default workspace created on gateway startup for backwards compatibility
• Workspace-scoped resources: workspace field on ObjectMeta — sandboxes, providers, service endpoints, SSH sessions, policies, settings, provider refresh state, and inference routes all inherit workspace
  from context
• Membership model: AddWorkspaceMember, RemoveWorkspaceMember, ListWorkspaceMembers RPCs with (workspace, principal_subject) → role records; membership records cleaned up on workspace deletion
• Persistence: Name uniqueness shifts from (object_type, name) to (object_type, workspace, name) via migration 006; existing resources backfilled to default workspace; cross-workspace list_by_type store
  method for infrastructure operations (reconciler, resume, provider refresh)
• Provider profiles: Two-tier scoping with independent scope listing — workspace custom + built-in, or platform custom + built-in (no merged cross-scope view)
• Service routing: Endpoint hostnames include workspace prefix ({workspace}--{sandbox}--{service}.{domain}); default workspace preserves current format
• Inference routes: Rename Cluster* RPCs and messages to Route* (SetInferenceRoute, GetInferenceRoute, InferenceRouteConfig); workspace-scope route storage and lookup; derive workspace from sandbox
  principal for bundle resolution; thread --workspace through CLI inference commands
• ObjectWorkspace trait: requires_workspace() method with debug_assert! validation in store write helpers to catch empty-workspace bugs in debug builds
• CLI: --workspace and --all-workspaces flags on all resource commands; WORKSPACE column as first column in list outputs when --all-workspaces (matching kubectl --all-namespaces convention); workspace
  CRUD and membership subcommands; inference help text updated from "gateway-level" to "workspace-level"
• TUI: Workspace state with [w] key cycling, WORKSPACE column in sandbox/provider tables, workspace indicator in title bar, workspace-scoped gRPC requests

Related Issue

#1977

Changes

• 50 files changed, +7188 / -886 lines
• New files: workspace.rs (gRPC handlers + tests), migration 006 (sqlite + postgres), workspace_lifecycle.rs (e2e test), RFC 0011
• Proto: Workspace, WorkspaceMember messages; workspace CRUD and membership RPCs; workspace field on ObjectMeta; all_workspaces on list requests; inference route rename (Cluster* → Route*) with
  workspace fields on set/get request/response messages

Testing

• 897 server unit tests passing (11 workspace-specific, 2 inference route workspace isolation)
• 24 TUI tests passing
• 7 CLI integration tests passing
• e2e workspace lifecycle test covering create/list/get/delete and cross-workspace isolation
• Inference route isolation tests: verify workspace-scoped route resolution (alpha/beta workspaces with different providers/models) and empty bundle for workspace with no route configured

Known remaining work

• Phase 2: Expanded role model (Platform Admin / Workspace Admin / User) and authorization enforcement — not started, sequential dependency on this PR.

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[sjenning]

From CodeRabbit review:
Include SSH sessions in workspace deletion blockers.

ObjectWorkspace for SshSession marks sessions as workspace-scoped, but deletion does not check SshSession::object_type(). A workspace can therefore be removed while session records still reference it.

     for (object_type, label) in [
         (Sandbox::object_type(), "sandbox"),
         (Provider::object_type(), "provider"),
+        (SshSession::object_type(), "SSH session"),
         (ServiceEndpoint::object_type(), "service"),
         (InferenceRoute::object_type(), "inference route"),
     ] {