Remove completed roadmap documentation

docs/roadmap/workspace.md

@@ -1,14 +0,0 @@
-# Workspace Future Work
-
-Current workspace settings and operating behavior are documented in
-[Configuration](../config.md#workspace) and
-[Operations](../operations.md). This roadmap contains only candidate additions
-to that behavior.
-
-## Candidate Work
-
-- Default-idempotent run behavior with an explicit force override.
-- Remote workspace storage.
-- Workspace garbage collection.
-- Workspace archival policy.
-- Cross-machine checkpoint reuse.