fix(tui): align switch reminders

[opencode-agent]

Summary

• keep instruction reminder alignment unchanged
• indent agent/model/variant switch reminders to match instruction reminders
• cover switch/instruction alignment with a renderer test

Checks

• cd packages/tui && bun test test/cli/tui/inline-tool-wrap-snapshot.test.tsx
• cd packages/tui && bun typecheck
• real TUI simulation: changed instructions, switched to the medium variant, then submitted another prompt and verified both reminders align

Note

• The repo-wide pre-push typecheck still hits an unrelated existing packages/app/src/context/server-sdk.test.ts cast error on origin/v2; the changed TUI package typecheck passes.