walker: flag LIKE on a numeric column (ADR-0027 Amendment 1)

LIKE is a text-pattern match; against a numeric column (int,
real, decimal, serial) it runs but is almost never intended.
predicate_warnings now emits a WARNING for it, spanned at the
target column. New Type::is_numeric; catalog key
diagnostic.like_numeric; ADR-0027 gains "Amendment 1" and the
adr/README index line is updated per the index-upkeep rule.

bool and the text-/blob-backed types are deliberately not
flagged — see the amendment for the rationale.

3 walker tests (int, decimal NOT LIKE, text-column clean).
1108 passing, clippy clean.

src/friendly/keys.rs

@@ -39,6 +39,7 @@
 pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
     // ---- Pre-submit diagnostics (ADR-0027) ----
     ("diagnostic.eq_null", &[]),
+    ("diagnostic.like_numeric", &["column", "type"]),
     ("diagnostic.type_mismatch", &["column", "type"]),
     ("diagnostic.unknown_column", &["name", "table"]),
     ("diagnostic.unknown_table", &["name"]),