Closes the resolver's second deferred wall. The resolver now lowers
`r.f(args…)` to a new `ExprKind::MethodCall` (receiver + interned method
name with its own span + args) instead of a spanned `Unsupported`
placeholder; the type checker walks it with the receiver's type in hand
and resolves the trait the call sugars to.

Resolution (`ck_types::method_call`): a trait method's receiver is its
first explicit parameter (no privileged `self`), so a call matches a
method whose param list has `args.len() + 1` entries. Candidate traits
come from the coherence table for a concrete `Ty::Nominal` receiver, or
the enclosing `where`-bounds for a `Ty::Var` receiver, intersected with
the new project-global `TraitMethodTable` (`build_trait_methods`, a
front-loaded pass like the coherence/field tables). Exactly one →
recorded in `TypeckResults::resolved_method` as `(TraitId, Symbol)` and
typed as the method's return; zero → E0728; many → E0729; a `Nothing`
receiver → E0720 (dead code, shared with TY7); `Unknown` → fail-soft.

Diagnostic codes reassigned from the design draft (E0713/E0714 went to
L1 list literals): E0728 method-not-found, E0729 ambiguous, E0720
Nothing-receiver. E0725 (closed existential) deferred to TY8.

Deferred (v0): receiver-vs-first-param assignability check, and
return-type-parameter substitution (a method returning the trait's own
type param types `Unknown`; gating fixtures return concrete types).

Goldens: method_call_rewrite / method_call_via_bound / ambiguous_method
/ unknown_method. Conformance ratchet 113→112 (with_effect_clause's
`line.bytes()` now fires E0728 and gained a trap block). Gates green:
build, clippy -D warnings, full test suite.

@@ -586,0 +721,4 @@
+        );
+        let (_, tail) = root_block(&body);
+        let ExprKind::With { base, value } = body.expr(tail.expect("trailing with")).kind else {
+            panic!("expected a With, got {:?}", body.expr(tail.unwrap()).kind);

@@ -0,0 +365,4 @@
+/// means a wrong receiver neither resolves nor causes a spurious ambiguity:
+/// exactly one accepting → resolved; many → **E0729**; none, but a match was
+/// rejected only on the receiver → **E0702**; no match at all → **E0728**.
+fn select_candidate(matches: Vec<Candidate>, recv_ty: &Ty) -> MethodResolution {

@@ -0,0 +244,4 @@
+    // pass; the receiver slot (and its E0702 secondary label) is the *last*
+    // parameter under data-last binding.
+    let mut params: Vec<Ty> = Vec::new();
+    let mut param_idents: Vec<ParamIdent> = Vec::new();