[nima-boltz]

• Fix empty State, Database, and Metadata panels after selecting Use legacy inspector. The fallback wrapper fills the detail pane, but its child tab layout cannot grow because the wrapper is a block container. Make that wrapper a flex column.
• Reproduced with Engine 2.3.30 and RivetKit 2.3.26: prevent /inspector/ui/ from loading, select the legacy fallback, and open State. On unchanged main, the JSON is present but the content panel measures 0 px. With this change, the same panel measures 674 px and displays the JSON.
• Verified the OSS production build in Chrome and checked formatting. The frontend suite reports 69 passing tests plus a load failure in src/lib/errors.test.ts (localStorage.getItem is unavailable); the same failure occurs on unchanged main under Node 22.
• Draft pending the cloud visual check required by the frontend contribution guidance. The normal iframe inspector is unchanged.