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/data.rs

@@ -38,6 +38,7 @@ const TABLE_NAME_EXISTING: Node = Node::Ident {
     writes_table: false,
     writes_column: false,
         writes_user_listed_column: false,
+writes_table_alias: false,
 };
 
 /// Table-name slot variant that populates
@@ -52,6 +53,7 @@ const TABLE_NAME_INSERT: Node = Node::Ident {
     writes_table: true,
     writes_column: false,
         writes_user_listed_column: false,
+writes_table_alias: false,
 };
 
 // =================================================================
@@ -110,6 +112,7 @@ static FORM_A_COLUMN: Node = Node::Ident {
     writes_table: false,
     writes_column: false,
     writes_user_listed_column: true,
+writes_table_alias: false,
 };
 static INSERT_COMMA: Node = Node::Punct(',');
 
@@ -221,6 +224,7 @@ const TABLE_NAME_WRITES: Node = Node::Ident {
     writes_table: true,
     writes_column: false,
         writes_user_listed_column: false,
+writes_table_alias: false,
 };
 
 /// Column-name slot in `set col = …` — resolves the column's
@@ -234,6 +238,7 @@ const SET_COLUMN: Node = Node::Ident {
     writes_table: false,
     writes_column: true,
     writes_user_listed_column: false,
+writes_table_alias: false,
 };
 
 /// Value slot resolved at walk time from
@@ -389,6 +394,7 @@ const SELECT_ALIAS_IDENT: Node = Node::Ident {
     writes_table: false,
     writes_column: false,
     writes_user_listed_column: false,
+writes_table_alias: false,
 };
 static SELECT_AS_ALIAS_NODES: &[Node] = &[
     Node::Word(Word::keyword("as")),
@@ -432,6 +438,7 @@ const SELECT_FROM_TABLE: Node = Node::Ident {
     writes_table: true,
     writes_column: false,
     writes_user_listed_column: false,
+writes_table_alias: false,
 };
 
 /// `where <sql_expr>`.