Clarify plugin browse categories

[brsbl]

Summary

• remove the redundant BB Official catalog container so categories render directly
• define one authoritative curated category order for all 13 bundled plugins
• preserve existing cards, install state, detail navigation, loading, error, empty, and search behavior
• keep the legacy Settings browse projection consistent without changing extension experiment behavior

Category structure

• Workflow management: Automations, Tasks, Workflows
• Agent interaction: Ask User Question, Side chat
• Context & knowledge: Custom instructions, Docs, Memory
• Developer tools: GitHub, Secrets
• Host access: Remote access
• Interface: Inline visualizations, t3sidebar

Verification

• pnpm exec turbo run test --filter=@bb/app -- --run src/components/plugin/management/BrowsePluginsTab.test.tsx src/components/plugin/PluginsOverview.test.tsx src/components/settings/plugins/BrowsePluginsTab.test.tsx — 15 passed
• pnpm exec turbo run test --filter=@bb/server -- --run test/services/plugin-catalog/plugin-catalog-service.test.ts test/services/plugins/official-plugins.test.ts — 13 passed
• pnpm exec turbo run typecheck --filter=@bb/app --filter=@bb/server — passed
• branch dev app visually verified at the top and bottom of the catalog plus a Memory-filtered result; all 13 cards render exactly once in category order
• git diff --check — passed

Stacked on #976. Not merged.