feat(hint): H2 Phase C batch 2 — DDL tier-3 hints (ADR-0053)

Per-form hints for the schema-shaping commands: create table, create
m:n, add column/index/constraint, drop table/column/relationship/
index/constraint, rename column, change column (add_relationship was
the Phase-B exemplar). Examples verified against the canonical usage
templates. hint_ids wired on CREATE/CREATE_M2N/DROP/RENAME/CHANGE;
catalogue + keys.rs registered. +2 spot tests (incl. multi-form DROP
disambiguation); 2491 pass / 1 ignored, clippy clean.

src/dsl/grammar/mod.rs

@@ -917,9 +917,12 @@ mod hint_key_tests {
             hint_key_for_input_in_mode("insert into T values (1)", Mode::Simple),
             Some("insert")
         );
-        // A node with no hint_ids yet → None (tier-2 fallback).
-        assert_eq!(hint_key_for_input_in_mode("drop table T", Mode::Simple), None);
-        // Unknown entry word → None.
+        // Multi-form DROP disambiguates to the typed form too.
+        assert_eq!(
+            hint_key_for_input_in_mode("drop table T", Mode::Simple),
+            Some("drop_table")
+        );
+        // Unknown entry word → None (tier-2 fallback).
         assert_eq!(hint_key_for_input_in_mode("zzz", Mode::Simple), None);
     }
 }