feat: ADR-0035 4a — SQL CREATE TABLE command, worker, and exit gate

Command + builder + worker for advanced-mode SQL CREATE TABLE
(sub-phase 4a), executed structurally through do_create_table:

- Command::SqlCreateTable + build_sql_create_table (ddl.rs): aliases via
  from_sql_name (incl. double precision), column- and table-level
  PRIMARY KEY, redundant-flag de-dup off a sole PK, IF NOT EXISTS.
  Advanced REGISTRY entry on the shared `create` word (SQL-first, DSL
  fallback); no-PK tables allowed (user-confirmed).
- Worker (db.rs): Request::SqlCreateTable + CreateOutcome + snapshot_then
  (one undo step); IF NOT EXISTS no-op (no snapshot, but journalled, like
  read-only commands). do_create_table inline-PK rule aligned with the
  rebuild generator schema_to_ddl — no round-trip DDL drift; serial
  autoincrement is independent of inline-PK (verified by round-trip
  tests).
- Runtime/App: dispatch + CommandOutcome::SchemaSkipped +
  AppEvent::DslCreateSkipped (structure + "already exists — skipped"
  note). Friendly catalog keys added (engine-neutral).

DEFAULT/CHECK/table-level UNIQUE are absent from the 4a grammar (parse
error with usage skeleton; friendly message + support land in the 4a.2
constraint slice) — user-confirmed.

Tests: type resolver, grammar shape, builder (incl. the PK
detection bug they caught), and tests/sql_create_table.rs (worker
round-trip, serial autoincrement first/non-first across rebuild, IF NOT
EXISTS no-op + journalling, no-PK table, one undo step) + a replay-as-
write test. 1739 pass / 0 fail / 1 ignored; clippy clean.

Exit gate: ADR-0035 Proposed -> Accepted (validated end-to-end by 4a);
README + requirements.md Q1 updated.

src/runtime.rs

@@ -29,8 +29,8 @@ use crate::action::Action;
 use crate::app::App;
 use crate::cli::Args;
 use crate::db::{
-    AddColumnResult, ChangeColumnTypeResult, DataResult, Database, DbError, DeleteResult,
-    DropColumnResult, InsertResult, QueryPlan, TableDescription, UpdateResult,
+    AddColumnResult, ChangeColumnTypeResult, CreateOutcome, DataResult, Database, DbError,
+    DeleteResult, DropColumnResult, InsertResult, QueryPlan, TableDescription, UpdateResult,
 };
 use crate::dsl::{Command, ColumnSpec};
 use crate::dsl::walker::Severity;
@@ -1253,6 +1253,10 @@ fn spawn_dsl_dispatch(
                 command: command.clone(),
                 description,
             },
+            Ok(CommandOutcome::SchemaSkipped(description)) => AppEvent::DslCreateSkipped {
+                command: command.clone(),
+                description,
+            },
             Ok(CommandOutcome::Query(data)) => AppEvent::DslDataSucceeded {
                 command: command.clone(),
                 data,
@@ -1645,6 +1649,11 @@ fn parse_qualified_target(message: &str) -> Option<(String, String)> {
 
 enum CommandOutcome {
     Schema(Option<TableDescription>),
+    /// A SQL `CREATE TABLE IF NOT EXISTS` that matched an existing
+    /// table — a no-op (ADR-0035 §4). Carries the existing structure
+    /// so the App can render it alongside the "already exists —
+    /// skipped" note.
+    SchemaSkipped(TableDescription),
     Query(DataResult),
     QueryPlan(QueryPlan),
     Insert(InsertResult),
@@ -1911,6 +1920,18 @@ async fn execute_command_typed(
             .create_table(name, columns, primary_key, src)
             .await
             .map(|d| CommandOutcome::Schema(Some(d))),
+        Command::SqlCreateTable {
+            name,
+            columns,
+            primary_key,
+            if_not_exists,
+        } => database
+            .sql_create_table(name, columns, primary_key, if_not_exists, src)
+            .await
+            .map(|outcome| match outcome {
+                CreateOutcome::Created(d) => CommandOutcome::Schema(Some(d)),
+                CreateOutcome::Skipped(d) => CommandOutcome::SchemaSkipped(d),
+            }),
         Command::DropTable { name } => database
             .drop_table(name, src)
             .await