DSL parser, async DB worker, types, history, metadata, polish

Track 1 implementation plus polish round.

Parser (chumsky):
- Grammar-based DSL producing a typed Command AST.
- create table X with pk [name:type[,name:type...]] supports
  arbitrary names, any user type, compound PKs natively. Bare
  form errors with a friendly hint pointing at `with pk`.
- add column to table X: Name (type); drop table X.
- Required clauses use keyword grammar; -- reserved for opt-in
  flags (ADR-0009). Custom Rich reasons preferred when surfacing
  chumsky errors so unknown-type messages list valid alternatives.

Database (ADR-0010, ADR-0012):
- rusqlite + STRICT tables + foreign_keys=ON.
- Dedicated worker thread; mpsc Request inbox, oneshot replies.
- Typed DbError with friendly_message() hook for H1.
- Internal __rdbms_playground_columns metadata table preserves
  user-facing types across schema reads, atomically maintained
  alongside DDL via Connection transactions. list_tables hides
  it via the new __rdbms_ internal-table convention.

Types (ADR-0005, ADR-0011):
- All ten user-facing types: text, int, real, decimal, bool,
  date, datetime, blob, serial, shortid.
- Type::fk_target_type() for FK-side column-type rule
  (Serial->Int, ShortId->Text, others identity) -- foundation
  for the FK iteration.

App / Runtime / UI:
- update() stays pure-sync; runtime dispatches DSL via spawned
  tasks, results post back as AppEvent::Dsl*.
- Items panel renders live tables list; output panel shows the
  user-facing structure of the current table after each DDL.
- In-memory command history (Up/Down, draft preservation,
  consecutive-duplicate dedup) -- I2 partial.
- Mouse capture removed; terminal native text selection
  restored (toggle approach revisited when scroll/click
  features land).

Docs:
- ADRs 0009 (DSL syntax conventions), 0010 (DB worker),
  0011 (FK type compat), 0012 (internal metadata table).
- requirements.md progress notes; new V4 entry for the
  scrollable session-log + inline rich rendering + Markdown
  export direction.

Tests: 103 passing (91 lib + 12 integration), 0 skipped.
Clippy clean with nursery enabled.

docs/requirements.md

@@ -48,6 +48,8 @@ against it.
 - [ ] **S2** Items list shows tables and per-table indexes;
   designed to extend to additional element kinds (relations,
   views, etc.) without restructuring.
+  *(Progress: tables are listed live from the database; indexes
+  pending alongside C3 index support.)*
 - [ ] **S3** Output panel renders a visualization of the
   currently selected item and supports multiple tabs.
 - [ ] **S4** Hint area below the input field; keyboard-toggleable
@@ -61,6 +63,10 @@ against it.
   equivalent) submits, plain Enter inserts a newline.
 - [ ] **I2** Persistent navigable input history (project-scoped,
   with a global rolling history also available).
+  *(Progress: in-memory navigable history (Up/Down arrows, draft
+  preservation, dedup of consecutive duplicates) is implemented;
+  persistence across sessions arrives with track 2's project
+  storage.)*
 - [ ] **I3** Tab completion for app commands, DSL keywords, table
   names, column names, and SQL keywords.
 - [ ] **I4** Syntax highlighting for both the DSL and SQL.
@@ -85,16 +91,24 @@ against it.
   available in both modes: `save`, `save as`, `load`, `new`,
   `export`, `import`, `seed`, `replay`, `undo`, `redo`, `mode`,
   `help`, `hint`, `quit`.
+  *(Progress: `quit`/`q` and `mode simple|advanced` implemented;
+  the rest land alongside the features they belong to — `save`
+  and friends in track 2, `seed` in the seeding iteration, etc.)*
 
 ## DSL data commands
 
 - [ ] **C1** Table operations: create / drop / rename.
+  *(Progress: create + drop done; rename pending.)*
 - [ ] **C2** Column operations: add / drop / rename / change
   type, including the rebuild-table dance behind the scenes
   where SQLite ALTER cannot do it directly.
+  *(Progress: add done; drop/rename/change-type pending — the
+  rebuild-table dance is the gating piece, B2.)*
 - [ ] **C3** Schema constraints: primary key (single and
   compound), foreign key with `ON DELETE` / `ON UPDATE` referential
   actions, indexes, `NOT NULL`, `UNIQUE`, `CHECK`, `DEFAULT`.
+  *(Progress: PK including compound done at create-table time;
+  FK/index/NOT NULL/UNIQUE/CHECK/DEFAULT pending.)*
 - [ ] **C4** Convenience: `create m:n relationship from <T1> to
   <T2>` produces an auto-named junction table the user can rename;
   pulls primary keys and FK definitions automatically.
@@ -104,31 +118,43 @@ against it.
 
 - [ ] **Q1** SQL parsed via `sqlparser-rs`; supported subset is
   defined (specifics deferred to a future ADR).
+  *(Progress: DSL is parsed via `chumsky` (ADR-0009); SQL
+  handling in advanced mode is still a placeholder echo.)*
 - [ ] **Q2** Non-standard syntax rejected with a clear message
   pointing at the supported subset.
-- [ ] **Q3** User-facing simplified types map transparently to
-  SQLite STRICT types in generated DDL.
+- [x] **Q3** User-facing simplified types map transparently to
+  SQLite STRICT types in generated DDL. *(All ten types implemented
+  and tested.)*
 - [~] **Q4** Supported SQL subset specification — design and ADR
   pending. Q1 cannot be marked satisfied without it.
 
 ## Database backend (per ADR-0002)
 
-- [ ] **B1** SQLite via `rusqlite`; all tables created `STRICT`;
-  `PRAGMA foreign_keys = ON` per connection.
+- [x] **B1** SQLite via `rusqlite`; all tables created `STRICT`;
+  `PRAGMA foreign_keys = ON` per connection. *(Database accessed
+  through a dedicated worker thread per ADR-0010.)*
 - [ ] **B2** Schema evolution uses the rebuild-table technique
   internally where SQLite `ALTER TABLE` cannot.
 - [ ] **B3** Query timeout and cancellation supported (no
   cartesian-join-of-doom can hang the app).
+  *(Progress: the worker-thread architecture is in place; the
+  cancellation/timeout protocol on top of it is pending.)*
 
 ## Type system (per ADR-0005)
 
-- [ ] **T1** All ten user-facing types implemented: `text`,
+- [x] **T1** All ten user-facing types implemented: `text`,
   `int`, `real`, `decimal`, `bool`, `date`, `datetime`, `blob`,
-  `serial`, `shortid`.
+  `serial`, `shortid`. *(Mapping to SQLite STRICT covered by
+  ADR-0005; FK target type rule by ADR-0011.)*
 - [ ] **T2** `shortid` generation: base58, 10–12 characters,
   omits ambiguous characters; generated client-side at insert.
+  *(Type exists; insert-time generation arrives with the data
+  insertion path.)*
 - [ ] **T3** Compound primary keys handled end-to-end (DSL,
   storage, display, FK reference).
+  *(Progress: DSL grammar (`with pk a:int,b:int`), storage, and
+  table-info description are all present; pretty display of the
+  PK in the structure view and FK reference still pending.)*
 
 ## Visualizations
 
@@ -136,10 +162,23 @@ against it.
   selected table as its structure (columns, types, keys,
   constraints); a selected relationship as two tables joined by
   a line.
+  *(Progress: a basic structure view (column rows with SQLite
+  type names) is rendered after each successful DDL; pretty
+  rendering, selection nav, and relationship line-art pending —
+  see V4 for the broader direction.)*
 - [ ] **V2** SQL query results render as a dynamic table view in
   the output pane, with multiple result tabs supported.
 - [~] **V3** Full ER-diagram export (whole-database graph, viewed
   outside the TUI) — low priority; design and ADR pending.
+- [~] **V4** Output panel as a *scrollable per-session log* with
+  inline rich rendering. Direction agreed in conversation: the
+  output area is a chronological journal of operations and
+  selections (e.g. a "selected table X" entry with the rendered
+  structure underneath); structure renderings choose between a
+  compact ASCII-table form and a vertical line-per-column form
+  based on dimensions; the log is exportable to Markdown so
+  learners can keep a record of their session. Design and ADR
+  pending before any implementation.
 
 ## Project lifecycle (per ADR-0004)