Fix workflow panel early-state spacing

[ymichael]

Human comments

What was wrong

The workflow thread panel uses the shared flush layout, so the plugin must own padding and scrolling in every state. Loading, initial RPC error, and no-run branches returned before any local spacing owner and rendered edge-to-edge, while the status primitives also added a second layer of margins, padding, borders, radius, and muted surface once the missing outer inset was restored.

What changed

Add one shared WorkflowRunPanelState frame that owns the 16px inset for invalid parameters and every early branch. Flatten the loading and empty/error primitives so they own only their semantic content and skeleton layout. Add a table-driven regression for the three asynchronous early states and a real SDK-backed Ladle story covering all non-loaded states plus a terminal loaded run. Loaded scrolling, terminal/footer behavior, the host flush contract, wire contracts, CLI surfaces, and public Plugin SDK APIs are unchanged.

How you verified

• Original focused red: 3 failed / 17 passed before the outer-inset fix
• Cleanup focused red: the same 3 cases failed before nested state chrome was removed
• pnpm exec turbo run test --filter=bb-plugin-workflows --force (13 files, 226/226 passed)
• pnpm exec turbo run typecheck --filter=bb-plugin-workflows
• pnpm exec turbo run typecheck --filter=@bb/app
• git diff --check origin/main...HEAD
• DevBrowser computed-style checks at 360px: 16px outer inset, zero inner margin/padding/border/radius, and transparent inner background for every early state
• Loaded content retained its 16px inset, exact scroll behavior, no horizontal overflow, and no terminal footer
• React performance audit: the production wrapper is static; the story effect uses stable module-level dependencies and performs complete slot cleanup

AGENT GENERATED