fix(ci): restore explore frontend checks

[wgqqqqq]

Summary

• update the Task execution boundary contract to require the policy-aware child_delegation_policy path used by Ultra Swarm
• protect both background launches and foreground execution, update the checker self-test, and add a regression against the obsolete bare spawn_child() path
• align the FlowChat typography contract with the composer-wide control role introduced by 56bc7bb30
• remove 14 stale appearance registrations that had no corresponding DOM contract on 1.0.0-explore

Root cause

1.0.0-explore had three pre-existing CI contract mismatches:

1. Ultra Swarm replaced bare delegation_policy().spawn_child() with policy-aware child delegation, but the required-content rule still searched for the old expression.
2. The composer typography was intentionally unified on the control role, while the placeholder contract still expected the former body role.
3. Appearance descriptors retained parts removed from the rendered DOM (Markdown reproduction parts, UserMessageItem.blocks, and SessionConfig debug/template parts), so the appearance contract audit rejected the base.

The clean 1.0.0-explore base failed on the first mismatch. Once that stage passed, CI exposed the typography test and then the appearance audit.

Verification

• pnpm run check:core-boundaries:test (121/121 passed)
• pnpm run check:core-boundaries
• pnpm --dir src/web-ui run test:run src/flow_chat/components/FlowChatTypographyRoles.test.ts (3/3 passed)
• pnpm run appearance:contract-audit
• pnpm run build:web (type generation, TypeScript, Vite build, Monaco assets, WebKit compatibility)
• git diff --check

This remains separate from #2378 so the target branch CI baseline is repaired independently.