fix(agent-chat): keep pending approvals recoverable

[zhangjiadi225]

Summary

• make non-dismissible bottom sheets use a programmatic-only closed detent while preserving controlled closes
• collapse a dismissed tool approval into a tappable recovery bar over the still-mounted composer
• subscribe to pending approvals through a narrow Session selector and keep approve or deny as the only resolving actions
• add regression coverage and document the approval presentation lifecycle

Validation

• pnpm format
• pnpm exec oxlint <changed TypeScript files>
• pnpm exec expo lint <changed TypeScript files>
• git diff --check origin/v0.2...HEAD

Notes

• Full pnpm lint reaches Expo ESLint but cannot resolve the unbuilt @cherrystudio/ai-core package in seven unchanged backend files; targeted Oxlint and Expo lint pass for every changed TypeScript file.
• Tests, typecheck, and device UI verification were not run per the repository verification policy.