refactor: rename workspace adapters

[kitlangton]

Summary

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

Replaces #25025.

Testing

• bun typecheck (packages/opencode)
• bun typecheck (packages/plugin)
• bun typecheck (packages/sdk/js)
• ./packages/sdk/js/script/build.ts
• bun run test test/control-plane/adapters.test.ts test/control-plane/workspace.test.ts test/plugin/workspace-adapter.test.ts test/server/httpapi-instance-context.test.ts test/server/httpapi-session.test.ts test/server/httpapi-workspace-routing.test.ts test/server/httpapi-workspace.test.ts (packages/opencode)