walker: populate cte_bindings placeholders + projection_aliases (ADR-0032 §10.3 stage 1 / §10.4)

Sub-phase 2b checkpoints 4 and 5 combined — adds the
placeholder CTE binding push (§10.3 stage 1) and the
projection alias accumulator (§10.4).

Node::Ident gains two more flags, mechanically applied to
every existing site:

- `writes_cte_name: bool` — push a placeholder `CteBinding`
  (name only, empty columns) onto the top `ScopeFrame`'s
  `cte_bindings`. Set on `CTE_NAME_IDENT` in sql_select.rs.
  Fires BEFORE the body's `ScopedSubgrammar` enters (the
  CTE-def Seq's ident slot precedes the body's `(`), so the
  body can self-reference the CTE name as a valid table source
  (WITH RECURSIVE).
- `writes_projection_alias: bool` — append the matched name to
  the top frame's `projection_aliases`. Set on
  `PROJECTION_BARE_ALIAS_IDENT` so both the AS-form
  (`a AS alpha`) and bare-form (`a alpha`) paths capture
  cleanly. The ident is shared by both paths through
  `PROJECTION_AS_ALIAS` and the lookahead factory, so
  capturing on the ident itself covers both forms with no
  duplication.

The §10.3 stage-2 harvest (deriving CTE output columns from the
body's projection per the six derivation rules in the ADR's
table) is structurally deferred — the placeholder's `columns`
stays empty until the harvest is wired. This is intentional
scope honesty: the placeholder-name presence is sufficient for
the schema-existence diagnostic (2d) to recognize CTE names as
valid table sources, and the qualified-prefix completion (2e)
will populate the columns when the harvest hook is added there.
Tests below assert the placeholder-name behavior; the
column-derivation tests from plan §2b's exit gate will be
satisfied incrementally as later sub-phases need them.

Tests (8 new, all green):

- Single CTE → one placeholder binding with the matched name.
- Multiple CTEs → placeholders in declaration order.
- Recursive CTE → name visible inside body (the body's
  `from r` reference parses; verified by the walk completing).
- Projection aliases via AS form → captured into the top
  frame's `projection_aliases`.
- Projection aliases via bare form → captured.
- Mixed alias forms → captured in projection order, with
  unaliased projection items absent from the alias list.
- No aliases → empty `projection_aliases`.
- CTE body aliases do not leak to outer scope (the body's
  frame pops on `ScopedSubgrammar` exit, taking its
  projection_aliases with it).

All 1358 previous tests still pass. Test totals: 1366
passing, 0 failed, 1 ignored. Clippy clean.

This closes out the scope-accumulator side of sub-phase 2b.
The remaining 2b-style work — full CTE column-derivation
harvest per §10.3's six rules — folds into 2d (where the
arity-check pass needs declared-vs-derived column counts) and
2e (where qualified-prefix completion needs CTE columns).

src/dsl/grammar/sql_select.rs

@@ -198,9 +198,10 @@ fn table_source_bare_alias_factory(
 // Alias slot
 // =================================================================
 
-/// Projection-list alias slot. `writes_table_alias` stays
-/// `false` — the projection alias is not a table binding's
-/// alias. (Capture into `projection_aliases` lands in 2b-5.)
+/// Projection-list alias slot. `writes_projection_alias: true`
+/// pushes the matched name onto the top frame's
+/// `projection_aliases` so `ORDER BY` candidates can offer it
+/// (ADR-0032 §10.4).
 const PROJECTION_BARE_ALIAS_IDENT: Node = Node::Ident {
     source: IdentSource::NewName,
     role: "projection_alias",
@@ -210,6 +211,8 @@ const PROJECTION_BARE_ALIAS_IDENT: Node = Node::Ident {
     writes_column: false,
     writes_user_listed_column: false,
     writes_table_alias: false,
+    writes_cte_name: false,
+    writes_projection_alias: true,
 };
 
 /// Table-source alias slot — `writes_table_alias: true` so the
@@ -224,6 +227,8 @@ const TABLE_SOURCE_BARE_ALIAS_IDENT: Node = Node::Ident {
     writes_column: false,
     writes_user_listed_column: false,
     writes_table_alias: true,
+writes_cte_name: false,
+writes_projection_alias: false,
 };
 
 static PROJECTION_AS_ALIAS_NODES: &[Node] = &[
@@ -268,6 +273,8 @@ const QUALIFIED_STAR_QUALIFIER: Node = Node::Ident {
     writes_column: false,
     writes_user_listed_column: false,
 writes_table_alias: false,
+writes_cte_name: false,
+writes_projection_alias: false,
 };
 
 static QUALIFIED_STAR_NODES: &[Node] = &[
@@ -348,6 +355,8 @@ const TABLE_NAME_IDENT: Node = Node::Ident {
     writes_column: false,
     writes_user_listed_column: false,
     writes_table_alias: false,
+writes_cte_name: false,
+writes_projection_alias: false,
 };
 
 static TABLE_SOURCE_NODES: &[Node] = &[
@@ -581,7 +590,9 @@ const CTE_NAME_IDENT: Node = Node::Ident {
     writes_table: false,
     writes_column: false,
     writes_user_listed_column: false,
-writes_table_alias: false,
+    writes_table_alias: false,
+    writes_cte_name: true,
+    writes_projection_alias: false,
 };
 
 const CTE_COLUMN_IDENT: Node = Node::Ident {
@@ -593,6 +604,8 @@ const CTE_COLUMN_IDENT: Node = Node::Ident {
     writes_column: false,
     writes_user_listed_column: false,
 writes_table_alias: false,
+writes_cte_name: false,
+writes_projection_alias: false,
 };
 
 static CTE_COLUMN_LIST_NODES: &[Node] = &[