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/app.rs

@@ -442,6 +442,23 @@ impl App {
                 self.handle_dsl_success(&command, description);
                 Vec::new()
             }
+            AppEvent::DslCreateSkipped {
+                command,
+                description,
+            } => {
+                // No-op (CREATE TABLE IF NOT EXISTS on an existing
+                // table, ADR-0035 §4): the skip note, then the existing
+                // structure — no misleading "[ok] create table" line.
+                self.note_system(crate::t!(
+                    "ddl.create_skipped_exists",
+                    name = command.target_table()
+                ));
+                for line in crate::output_render::render_structure(&description) {
+                    self.note_system(line);
+                }
+                self.current_table = Some(description);
+                Vec::new()
+            }
             AppEvent::DslDataSucceeded { command, data } => {
                 self.handle_dsl_query_success(&command, &data);
                 Vec::new()
@@ -1533,6 +1550,9 @@ impl App {
         use crate::friendly::{Operation, TranslateContext};
         let (operation, fallback_table, fallback_column) = match command {
             C::CreateTable { name, .. } => (Operation::CreateTable, Some(name.as_str()), None),
+            C::SqlCreateTable { name, .. } => {
+                (Operation::CreateTable, Some(name.as_str()), None)
+            }
             C::DropTable { name } => (Operation::DropTable, Some(name.as_str()), None),
             C::AddColumn { table, column, .. } => (
                 Operation::AddColumn,