Walker: node-attached HintMode via Node::Hinted (ADR-0024 §HintMode-per-node)

Replaces the hint resolver's signature-matching (does the expected set
contain all five literal forms? an Ident{NewName}?) with a grammar-
declared annotation. New Node::Hinted { mode, inner } wrapper; the
walker records the mode in WalkContext::pending_hint_mode on entry and
clears it on any successful match (cursor moved past the slot — this
also undoes the leak where a failed Hinted branch of a Choice would
otherwise strand a stale mode). The resolver reads pending_hint_mode
directly.

Value-literal fallback slots carry ProseOnly; NewName ident slots carry
ForceProse. hint_mode_at_input_inner now delegates to
hint_resolution_at_input — one resolution path, no duplicated logic.
No behaviour change; the typing-surface matrix guards it.

src/dsl/grammar/shared.rs

@@ -7,7 +7,8 @@
 
 use crate::completion::TableColumn;
 use crate::dsl::grammar::{
-    IdentSource, IdentValidator, Node, NumberValidator, ValidationError, Word,
+    HintMode, IdentSource, IdentValidator, Node, NumberValidator,
+    ValidationError, Word,
 };
 use crate::dsl::types::Type;
 use crate::dsl::walker::context::WalkContext;
@@ -347,7 +348,16 @@ const FALLBACK_VALUE_LITERAL_CHOICES: &[Node] = &[
     Node::NumberLit { validator: None },
     Node::StringLit,
 ];
-const FALLBACK_VALUE_LITERAL: Node = Node::Choice(FALLBACK_VALUE_LITERAL_CHOICES);
+const FALLBACK_VALUE_LITERAL_INNER: Node = Node::Choice(FALLBACK_VALUE_LITERAL_CHOICES);
+/// The schemaless value-literal slot. The `ProseOnly` HintMode
+/// (ADR-0024 §HintMode-per-node) tells the hint resolver to
+/// surface the generic "Type a value: number, 'text', …" prose
+/// here rather than the misleading `null`/`true`/`false`
+/// candidate trio.
+const FALLBACK_VALUE_LITERAL: Node = Node::Hinted {
+    mode: HintMode::ProseOnly("hint.value_literal_slot"),
+    inner: &FALLBACK_VALUE_LITERAL_INNER,
+};
 
 const FALLBACK_VALUE_LIST: Node = Node::Repeated {
     inner: &FALLBACK_VALUE_LITERAL,
@@ -434,10 +444,3 @@ pub fn column_value_list(ctx: &WalkContext) -> Node {
     }
     Node::Seq(Box::leak(children.into_boxed_slice()))
 }
-
-// The HintMode / NumberValidator imports are part of the Phase D
-// typed-slot toolkit even though only NumberValidator is used by
-// the explicit validators above; surface HintMode so future
-// per-type prose annotations can attach without re-importing.
-#[allow(dead_code)]
-const _USES_HINT_MODE: Option<crate::dsl::grammar::HintMode> = None;