feat: bring simple-mode insert arity diagnostics to parity with advanced

A wrong-count simple-mode insert now shows the friendly per-column arity
message at typing time (instead of a bare "expected `,`/`)`") and is
blocked from dispatch at submit — unifying simple and advanced mode onto
the one ADR-0027 model (structural parse + ERROR diagnostic), where they
had diverged.

Grammar: a simple-mode-only arity gate (dsl_insert_value_list) routes a
wrong-count DSL insert tuple to the type-blind fallback so it matches
structurally and the per-tuple arity diagnostic fires. The gate is gated
to simple mode, so advanced behaviour is unchanged. count_tuple_values
and the target-column selection (insert_target_columns) are now shared
by both grammars.

Diagnostic: dml_insert_arity_diagnostics is mode-aware — advanced Form B
expects all columns; simple Form B/C expects the user-fillable columns
(serial/shortid auto-fill). It counts the DSL Form A role and scans the
keyword-less Form C tuple. New catalog keys name the fillable/auto split
and the all-auto-table case.

Submit: a wrong-count DSL insert now parses Ok + carries the ERROR
diagnostic, so a unified Ok-arm pre-flight (dsl_insert_count_mismatch_notes)
blocks dispatch and teaches; the previous Err-arm note retires.
advanced_alternative_note's gate now reads the validity verdict so it
still fires for the parse-Ok-with-error shape.

Docs: ADR-0036 Amendment 2 (+ README index) and requirements.md H1a.

src/friendly/keys.rs

@@ -51,6 +51,15 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
         "diagnostic.insert_arity_mismatch_form_b",
         &["expected", "actual"],
     ),
+    // ADR-0036 Amendment 1 / issue #17: simple-mode Form B variants.
+    (
+        "diagnostic.insert_arity_mismatch_form_b_simple",
+        &["expected", "columns", "skipped", "actual"],
+    ),
+    (
+        "diagnostic.insert_arity_mismatch_all_auto",
+        &["table", "actual"],
+    ),
     ("diagnostic.not_null_missing", &["column"]),
     ("diagnostic.like_numeric", &["column", "type"]),
     ("diagnostic.projection_alias_misplaced", &["alias", "clause"]),