constraints: CHECK-violation friendly error + typing-surface matrix (ADR-0029 §10)

Completes ADR-0029's implementation: the friendly-error layer
now names the rule a CHECK violation broke, and the
typing-surface matrix covers the whole constraint grammar.

CHECK-violation friendly error (ADR-0029 §10):
- enrich_dsl_failure gains a CHECK branch — it reads the column
  from the engine's `CHECK constraint failed: <column>`
  message, then resolves the table, the offending value, and
  the column's compiled CHECK expression.
- FailureContext / TranslateContext carry the resolved
  check_rule; translate_check renders "the value <v> breaks the
  rule `<rule>`" when it is known, falling back to the plain
  hint otherwise.

Typing-surface matrix: a new `constraints` submodule, 14 cells
covering the create-table / add-column constraint suffix and
the add-constraint / drop-constraint commands (174 → 188).

16 tests added (1 translate unit, 1 enrichment integration, 14
matrix cells).

src/friendly/keys.rs

@@ -50,8 +50,16 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
     // ---- CHECK violations ----
     ("error.check.insert.headline", &["table", "column"]),
     ("error.check.insert.hint", &["column"]),
+    (
+        "error.check.insert.hint_with_rule",
+        &["value", "rule", "column"],
+    ),
     ("error.check.update.headline", &["table", "column"]),
     ("error.check.update.hint", &["column"]),
+    (
+        "error.check.update.hint_with_rule",
+        &["value", "rule", "column"],
+    ),
     // ---- FK violations (anchor: "referenced by") ----
     (
         "error.foreign_key.child_side.insert.headline",