Constant PLAN_MODE_IMPLEMENT_REMINDER 

pub const PLAN_MODE_IMPLEMENT_REMINDER: &str = "• Still in Plan Mode (read-only). Say “implement” to execute, or “stay in plan mode” to revise. If automatic Plan->Edit switching fails, manually switch with `/plan off` or `/mode` (or press `Shift+Tab`/`Alt+M` in interactive mode).";

Shared reminder appended when presenting plans while still in Plan Mode.