walker: populate from_scope table bindings (ADR-0032 §10.1)

Sub-phase 2b checkpoint 3 — the `writes_table` / `writes_table_alias`
flags now drive the multi-binding `from_scope` accumulator on
the top `ScopeFrame`.

Node::Ident gains `writes_table_alias: bool`. When set on an
ident-name slot, the matched name lands on the most-recently-
pushed `TableBinding`'s `alias`. All 46 existing Ident sites
across the codebase are updated to `writes_table_alias: false`
(mechanical — no behavioral change for DSL paths).

walk_ident's `writes_table` semantics extend:

- `IdentSource::Tables` matches with `writes_table: true` still
  populate `current_table` / `current_table_columns` as before
  (preserved for DSL paths that read those fields directly via
  the dynamic-subgrammar / column-writes machinery), AND now
  also push a fresh `TableBinding` onto the top ScopeFrame's
  `from_scope`. The two mechanisms coexist additively —
  current_table reflects the most-recent `writes_table` write
  (single-binding view, as before); from_scope is the
  authoritative multi-binding accumulator that SQL JOINs,
  subqueries, and CTE bodies use.

sql_select.rs splits the alias slot into two ident variants:

- `PROJECTION_BARE_ALIAS_IDENT` (role `projection_alias`) —
  no scope writes; capture into `projection_aliases` is 2b-5.
- `TABLE_SOURCE_BARE_ALIAS_IDENT` (role `table_alias`,
  `writes_table_alias: true`) — sets the top binding's alias.

The `AS alias` form likewise splits into PROJECTION_AS_ALIAS
and TABLE_SOURCE_AS_ALIAS so each path threads through the
correct ident. The bare-alias lookahead factories return the
projection or table-source ident accordingly.

`TABLE_NAME_IDENT` in sql_select.rs gets `writes_table: true`
so each FROM / JOIN table source pushes a binding. The
schema-resolved columns are stored on the TableBinding for
later use by qualified-prefix completion (2e) and the
schema-existence diagnostic (2d).

Tests (9 new, all green):

- single from-table → one binding
- AS alias / bare alias on from-table → alias captured
- two-way JOIN → two bindings, correct order
- two-way JOIN with both aliased → two bindings with aliases
- three-way JOIN (left + bare) → three bindings in order
- subquery from_scope does not leak to outer scope (the
  ScopedSubgrammar push/pop discipline at work)
- CTE body from_scope does not leak to outer scope (the outer
  scope sees only the CTE-name reference, not the body's
  internals)
- SELECT without FROM → empty from_scope

All 1351 previous tests still pass — DSL paths untouched.
Test totals: 1358 passing, 0 failed, 1 ignored. Clippy clean.

Frame is_cte_body marker, body-projection harvest, and
projection_aliases population are the remaining 2b work
(2b-4 and 2b-5).

src/dsl/grammar/sql_select.rs

@@ -173,7 +173,7 @@ fn projection_bare_alias_factory(
         {
             Node::Subgrammar(&EMPTY_NOMATCH)
         }
-        Some(_) => BARE_ALIAS_IDENT,
+        Some(_) => PROJECTION_BARE_ALIAS_IDENT,
         None => Node::Subgrammar(&EMPTY_NOMATCH),
     }
 }
@@ -189,7 +189,7 @@ fn table_source_bare_alias_factory(
         {
             Node::Subgrammar(&EMPTY_NOMATCH)
         }
-        Some(_) => BARE_ALIAS_IDENT,
+        Some(_) => TABLE_SOURCE_BARE_ALIAS_IDENT,
         None => Node::Subgrammar(&EMPTY_NOMATCH),
     }
 }
@@ -198,24 +198,48 @@ fn table_source_bare_alias_factory(
 // Alias slot
 // =================================================================
 
-const BARE_ALIAS_IDENT: Node = Node::Ident {
+/// 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.)
+const PROJECTION_BARE_ALIAS_IDENT: Node = Node::Ident {
     source: IdentSource::NewName,
-    role: "select_alias",
+    role: "projection_alias",
     validator: None,
     highlight_override: None,
     writes_table: false,
     writes_column: false,
     writes_user_listed_column: false,
+    writes_table_alias: false,
 };
 
-static AS_ALIAS_NODES: &[Node] = &[
+/// Table-source alias slot — `writes_table_alias: true` so the
+/// matched name lands on the most-recently-pushed
+/// `TableBinding`'s `alias` (ADR-0032 §10.1).
+const TABLE_SOURCE_BARE_ALIAS_IDENT: Node = Node::Ident {
+    source: IdentSource::NewName,
+    role: "table_alias",
+    validator: None,
+    highlight_override: None,
+    writes_table: false,
+    writes_column: false,
+    writes_user_listed_column: false,
+    writes_table_alias: true,
+};
+
+static PROJECTION_AS_ALIAS_NODES: &[Node] = &[
     Node::Word(Word::keyword("as")),
-    BARE_ALIAS_IDENT,
+    PROJECTION_BARE_ALIAS_IDENT,
 ];
-static AS_ALIAS_EXPLICIT: Node = Node::Seq(AS_ALIAS_NODES);
+static PROJECTION_AS_ALIAS: Node = Node::Seq(PROJECTION_AS_ALIAS_NODES);
+
+static TABLE_SOURCE_AS_ALIAS_NODES: &[Node] = &[
+    Node::Word(Word::keyword("as")),
+    TABLE_SOURCE_BARE_ALIAS_IDENT,
+];
+static TABLE_SOURCE_AS_ALIAS: Node = Node::Seq(TABLE_SOURCE_AS_ALIAS_NODES);
 
 static PROJECTION_ALIAS_CHOICES: &[Node] = &[
-    Node::Subgrammar(&AS_ALIAS_EXPLICIT),
+    Node::Subgrammar(&PROJECTION_AS_ALIAS),
     Node::Lookahead(projection_bare_alias_factory),
 ];
 static PROJECTION_ALIAS_CHOICE: Node = Node::Choice(PROJECTION_ALIAS_CHOICES);
@@ -223,7 +247,7 @@ static PROJECTION_ALIAS_OPTIONAL: Node =
     Node::Optional(&PROJECTION_ALIAS_CHOICE);
 
 static TABLE_SOURCE_ALIAS_CHOICES: &[Node] = &[
-    Node::Subgrammar(&AS_ALIAS_EXPLICIT),
+    Node::Subgrammar(&TABLE_SOURCE_AS_ALIAS),
     Node::Lookahead(table_source_bare_alias_factory),
 ];
 static TABLE_SOURCE_ALIAS_CHOICE: Node =
@@ -243,6 +267,7 @@ const QUALIFIED_STAR_QUALIFIER: Node = Node::Ident {
     writes_table: false,
     writes_column: false,
     writes_user_listed_column: false,
+writes_table_alias: false,
 };
 
 static QUALIFIED_STAR_NODES: &[Node] = &[
@@ -319,9 +344,10 @@ const TABLE_NAME_IDENT: Node = Node::Ident {
     role: "table_name",
     validator: Some(reject_internal_table),
     highlight_override: None,
-    writes_table: false,
+    writes_table: true,
     writes_column: false,
     writes_user_listed_column: false,
+    writes_table_alias: false,
 };
 
 static TABLE_SOURCE_NODES: &[Node] = &[
@@ -555,6 +581,7 @@ const CTE_NAME_IDENT: Node = Node::Ident {
     writes_table: false,
     writes_column: false,
     writes_user_listed_column: false,
+writes_table_alias: false,
 };
 
 const CTE_COLUMN_IDENT: Node = Node::Ident {
@@ -565,6 +592,7 @@ const CTE_COLUMN_IDENT: Node = Node::Ident {
     writes_table: false,
     writes_column: false,
     writes_user_listed_column: false,
+writes_table_alias: false,
 };
 
 static CTE_COLUMN_LIST_NODES: &[Node] = &[