feat(ui): consolidate FlowChat presentation and design system

[GCWing]

Summary

• Consolidate FlowChat presentation into shared design-system components and the new private @openbitfun/flow-chat-presentation package.
• Align Web UI tool cards, grouping, thinking, scroll behavior, session interactions, brand assets, typography, and Design Lab examples with the shared presentation contracts.
• Update related agent queue/event contracts, installer styling, generated appearance assets, and localized copy.

Type and Areas

Type: Feature, UI/UX, refactor, regression fixes, tests.

Areas: Web UI, design system, FlowChat presentation, Rust coordination/events, CLI, installer.

Motivation / Impact

The current product changes make FlowChat presentation reusable across the app and Design Lab while preserving host-owned session behavior and accessibility. This PR contains the current code snapshot for review against main.

Verification

• pnpm.cmd install --frozen-lockfile --prefer-offline — passed.
• pnpm.cmd run fmt:rs — passed; no formatting changes.
• git diff --check — passed.
• pnpm.cmd run i18n:audit — passed.
• pnpm.cmd run check:repo-hygiene — passed.
• pnpm.cmd --filter @openbitfun/flow-chat-presentation run type-check — passed.
• pnpm.cmd --filter @openbitfun/flow-chat-presentation run test — 880 passed.
• Design-system builds and the corrected ContextLoadGroup test passed. The full design-system check is covered by CI.
• Web UI typography, Appearance, color, and theme visual checks passed. Web UI TypeScript passed after supplying local, gitignored API bindings in the isolated worktree.

Reviewer Notes

• Design, review, and process documentation were intentionally excluded. The only Markdown change is THIRD_PARTY_NOTICES.md, which describes the bundled font update.
• Verification was local. Remote workspace, remote control, Peer Device Mode, and Detached Dispatch were not exercised locally.
• No browser automation or mock screenshots were used for visual acceptance; visual review remains manual.

Checklist

• Temporary files and design/review documents are excluded from the commit.
• Relevant local verification is recorded above; CI will provide the broader checks.
• User-facing locale changes are included.