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/dsl/command.rs

@@ -122,6 +122,19 @@ pub enum Command {
     DropTable {
         name: String,
     },
+    /// Advanced-mode SQL `CREATE TABLE` (ADR-0035 §1, sub-phase 4a).
+    /// Its own command, but executed **structurally** through the
+    /// same `do_create_table` machinery as [`Self::CreateTable`] —
+    /// the columns / PK reuse `ColumnSpec`. `if_not_exists` makes an
+    /// already-existing table a no-op-with-note rather than an error
+    /// (ADR-0035 §4). 4a carries only `NOT NULL` / `UNIQUE` /
+    /// `PRIMARY KEY`; `DEFAULT` / `CHECK` are the 4a.2 slice.
+    SqlCreateTable {
+        name: String,
+        columns: Vec<ColumnSpec>,
+        primary_key: Vec<String>,
+        if_not_exists: bool,
+    },
     /// Add a column to an existing table. The column carries
     /// its constraints from the same suffix grammar as
     /// `create table` (ADR-0029); `check` is `None` until the
@@ -625,6 +638,7 @@ impl Command {
     pub const fn verb(&self) -> &'static str {
         match self {
             Self::CreateTable { .. } => "create table",
+            Self::SqlCreateTable { .. } => "create table",
             Self::DropTable { .. } => "drop table",
             Self::AddColumn { .. } => "add column",
             Self::DropColumn { .. } => "drop column",
@@ -673,6 +687,7 @@ impl Command {
     pub fn target_table(&self) -> &str {
         match self {
             Self::CreateTable { name, .. }
+            | Self::SqlCreateTable { name, .. }
             | Self::DropTable { name }
             | Self::ShowTable { name }
             | Self::ShowData { name, .. } => name,