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/strings/en-US.yaml

@@ -260,6 +260,9 @@ help:
   ddl:
     create: |-
         create table <T> with pk [<col>(<type>), ...]    — create a table
+    sql_create_table: |-
+        create table [if not exists] <T> (<col> <type> [not null] [unique] [primary key], ...
+          [, primary key (<col>, ...)])    — create a table (advanced SQL)
     drop: |-
         drop table <T>                                  — remove a table
         drop column [from] [table] <T>: <col> [--cascade]   — remove a column
@@ -368,6 +371,13 @@ hint:
   # explicit-column form so the skipped column is discoverable.
   value_slot_autogen_skipped: "({columns} auto-generated — skipped here; list columns explicitly, e.g. `insert into T (...) values (...)`, to set it.)"
 
+# Advanced-mode SQL DDL execution notes (ADR-0035).
+ddl:
+  # `create table if not exists <T>` where the table is already
+  # present: a no-op that succeeds with this note instead of an
+  # "already exists" error.
+  create_skipped_exists: "table '{name}' already exists — skipped (no changes made)"
+
 parse:
   # Wrapper around chumsky's structural error message. The
   # caret pointer (visualising the failure column) is printed
@@ -435,6 +445,7 @@ parse:
   # placeholders. ADR-0009's surface conventions apply.
   usage:
     create_table: "create table <Name> with pk [<col>(<type>)[, ...]]"
+    sql_create_table: "create table [if not exists] <Name> (<col> <type> [not null] [unique] [primary key], ... [, primary key (<col>, ...)])"
     drop_table: "drop table <Name>"
     drop_column: "drop column [from] [table] <Table>: <Name>"
     drop_relationship: |-