iter 22b.1.1: ClassDef/InstanceDef AST + downstream match arms

Adds Def::Class(ClassDef) and Def::Instance(InstanceDef) variants per
Decision 11 §"Form-A schema". All optional fields (superclass, doc,
default body) carry skip_serializing_if so canonical-JSON bytes of
pre-22b fixtures stay bit-identical.

Downstream match-on-Def sites are extended with explicit Class/Instance
arms. Behaviour for 22b.1 is placeholder (skip in typecheck/codegen,
one-line summary in pretty/manifest, placeholder marker in prose/print)
with TODO comments naming the deferred sub-iters (22b.2 typecheck,
22b.3 codegen, 22b.4 prose-projection arms).

crates/ail/src/main.rs

@@ -1007,6 +1007,14 @@ fn collect_refs(def: &ailang_core::Def) -> std::collections::BTreeSet<String> {
                 }
             }
         }
+        // Iter 22b.1: `ail deps` does not yet trace references inside
+        // class/instance defs. Walking method signatures and bodies
+        // (default bodies, instance method bodies) lands in 22b.2 along
+        // with the typecheck arms — until then a class/instance def
+        // contributes no entries to the dependency graph. Tools that
+        // call `collect_refs` (`ail deps`, the cross-module-fan-out
+        // diagnostics) therefore treat them as leaves.
+        ailang_core::Def::Class(_) | ailang_core::Def::Instance(_) => {}
     }
     out
 }
@@ -1416,6 +1424,25 @@ fn def_summary(d: &ailang_core::Def) -> (&'static str, String, Vec<String>) {
                 .join(" | ");
             ("type", s, vec![])
         }
+        // Iter 22b.1: a one-line `class C a` / `instance C T` summary
+        // for `ail manifest`. The `effects` slot is empty for both —
+        // class methods carry their own effect annotations on each
+        // method signature, but the class itself does not (it is a
+        // collection of method signatures, not a single function).
+        ailang_core::Def::Class(c) => (
+            "class",
+            format!("{} {}", c.name, c.param),
+            vec![],
+        ),
+        ailang_core::Def::Instance(i) => (
+            "instance",
+            format!(
+                "{} {}",
+                i.class,
+                ailang_core::pretty::type_to_string(&i.type_)
+            ),
+            vec![],
+        ),
     }
 }