fix(flow-chat): clarify permission scope menu

[GCWing]

Summary

• keep the current session permission modes as the primary single-select list, with a check only on the selected mode
• move next-message/current-turn permission choices into a click-open secondary level with Right/Left Arrow navigation
• add an explicit "Follow this session" choice to clear a one-off override while preserving existing permission behavior

Verification

• pnpm exec vitest run src/flow_chat/components/ChatInputWorkspaceStrip.test.tsx (30/30)
• pnpm run type-check:web
• pnpm run i18n:audit
• pnpm run appearance:contract-audit
• focused ESLint for the two changed source components
• git diff --check origin/1.0.0-explore...HEAD

Notes

• An earlier full pnpm run check:web attempt was blocked by pre-existing stale generated outputs for MiniApp Git Graph and native mobile token projection; those files are outside this six-file PR and were not modified.
• Browser/manual visual checks and E2E were not run, following the repository guidance for this focused menu change.