Settles the `hint` slot ADR-0003 left pending; closes the last open
piece of A1. Two surfaces (F1 → live-input hint; `hint` command →
last-error expansion), no topic arg, and a new tier-3 teaching corpus
keyed on a new CommandNode `hint_id` so advanced-SQL forms get distinct
mode-correct content. Comprehensive content for v1, authored
exemplars-first. Refines ADR-0003; references ADR-0019/0021/0022/0049/
0051. Files #36 for the parallel help-side gap.
claude@clouddev1