refactor: rename workspace adapters

[kitlangton]

Summary

• Rename workspace adaptor APIs, routes, and docs to adapter.
• Update plugin workspace types and registration helpers to use WorkspaceAdapter/registerAdapter.
• Regenerate SDK/OpenAPI output so the client uses experimental.workspace.adapter and /experimental/workspace/adapter.

Testing

• bun typecheck (packages/opencode)
• bun typecheck (packages/plugin)
• bun typecheck (packages/sdk/js)
• bun run test test/control-plane/adapters.test.ts test/plugin/workspace-adapter.test.ts test/server/httpapi-workspace.test.ts test/workspace/workspace-restore.test.ts (packages/opencode)

[kitlangton]

Superseded by #25272.