feat(design): resume conversations and repair document tool schema

[filipeforattini]

Add /design-open to resume an existing Design conversation through the same searchable modal pattern as /sessions. The picker shows prototype names, conversation titles and state, groups prototypes owned by the same conversation, and preserves its history and current agent. Design conversations that have not created a document yet remain discoverable. The modal explains that /design-review opens the preview after resuming.

The authenticated Design list is scoped to the current workspace and excludes archived or deleted sessions. Empty, loading, search-empty and HTTP error states stay inside the modal.

Also repair design_document's provider schema: advertise an object with a required action and explicit invocation guidance, then decode into the discriminated union before executing. TUI and Core share the contract. An HTTP regression through the actual OpenRouter SDK fails on the previous root anyOf schema and passes on this implementation. The exact cause of the reported GLM session's repeated {} calls remains unconfirmed without its trace.

Validation:

• Rendered TUI test covers command registration, search by conversation name, keyboard selection, resumption, draft/not-started labels and empty/error states.
• HTTP tests cover creation/review/approval, grouping, conversations without documents, workspace isolation and deleted sessions.
• 65 focused schema/tool tests passed for the document fix.
• bun typecheck passes in TUI, Schema, Core and Redcode.
• Includes patch changesets; release versions are unchanged.

The README now walks through the app-admin dark-mode example from prototype to browser feedback, approval, planning and implementation. It includes a workflow diagram, current command behavior and release availability, and separates regular TUI instructions from the optional Design terminal, where /resume has a different meaning.