Matrix: insert Form B coverage

12 tests across schema_serial_pk / text_pk / multi_table / every_type.
Pins (a) Form B skips auto-gen columns from the slot list (regression
for handoff-12 §B fix); (b) wrong-count value lists are now flagged
at typing time, not only at submit (the previous commit's fix); and
(c) per-type slot prose advances correctly through every Type variant.

tests/typing_surface/mod.rs

@@ -18,7 +18,7 @@ use rdbms_playground::completion::{
 use rdbms_playground::dsl::parser::parse_command_with_schema;
 use rdbms_playground::dsl::types::Type;
 use rdbms_playground::input_render::{
-    AmbientHint, InputState, ambient_hint, classify_input,
+    AmbientHint, InputState, ambient_hint, classify_input_with_schema,
 };
 
 pub mod insert_form_a;
@@ -168,7 +168,7 @@ pub struct Assessment {
 
 /// Assess the typing surface at the given cell.
 pub fn assess(input: &str, cursor: usize, schema: &SchemaCache) -> Assessment {
-    let state = classify_input(input);
+    let state = classify_input_with_schema(input, schema);
     let hint = ambient_hint(input, cursor, None, schema);
     let completion = candidates_at_cursor(input, cursor, schema);
     let parse_result = match parse_command_with_schema(input, schema) {