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/friendly/keys.rs

@@ -171,6 +171,9 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
     ("help.app.undo", &[]),
     ("help.app.redo", &[]),
     ("help.ddl.create", &[]),
+    ("help.ddl.sql_create_table", &[]),
+    // Advanced-mode SQL CREATE TABLE no-op note (ADR-0035 §4).
+    ("ddl.create_skipped_exists", &["name"]),
     ("help.ddl.drop", &[]),
     ("help.ddl.add", &[]),
     ("help.ddl.rename", &[]),
@@ -241,6 +244,7 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
     ("parse.usage.add_relationship", &[]),
     ("parse.usage.change_column", &[]),
     ("parse.usage.create_table", &[]),
+    ("parse.usage.sql_create_table", &[]),
     ("parse.usage.delete", &[]),
     ("parse.usage.drop_column", &[]),
     ("parse.usage.drop_constraint", &[]),