docs: website docs structure + first content pages

Phase D foundation. Configures the pragmatic four-section sidebar
(Getting started / Guides / Reference / Concepts) and replaces the
template example pages with grounded content built on the shared
"library" example database (authors/books/members/loans):

- Getting started: installation, first project, simple vs advanced,
  the example library.
- Reference: Types (all ten + serial/shortid + advanced aliases),
  Tables (create/drop, compound PK, advanced CREATE TABLE).
- Concepts: projects & storage (readable files, derived database,
  autosave, temp projects).
- Guides: Build the library (draft, to be refined for teaching).

Command syntax grounded in en-US.yaml usage/help, command.rs, and
types.rs (verified against tests). Records the settled doc decisions
in STYLE.md. Build green (10 pages, Pagefind); content clean of
"DSL"/engine-name.

website/src/content/docs/reference/tables.md

@@ -0,0 +1,92 @@
+---
+title: Tables
+description: Create and drop tables in simple mode and in advanced-mode SQL, including compound primary keys.
+sidebar:
+  order: 2
+---
+
+A table is the core building block. This page covers creating and removing
+tables; changing a table's columns after it exists is covered under Columns
+in the Reference.
+
+## Create a table (simple mode)
+
+Every table is created with its primary key. The `with pk` clause lists the
+primary-key column(s):
+
+```text
+create table authors with pk author_id(serial)
+```
+
+Other columns are added afterwards with `add column`:
+
+```text
+add column to authors: name (text)
+add column to authors: birth_year (int)
+```
+
+### Compound primary keys
+
+To make the primary key span more than one column, list them, comma
+separated:
+
+```text
+create table loans with pk book_id(int), member_id(int)
+```
+
+**Syntax**
+
+```text
+create table <Name> with pk <col>(<type>)[, ...]
+```
+
+## Create a table (advanced mode)
+
+In advanced mode you write a full `CREATE TABLE` with every column and
+constraint inline:
+
+```sql
+create table authors (
+  author_id serial primary key,
+  name text not null,
+  birth_year int
+)
+```
+
+The advanced form also accepts table-level constraints and inline foreign
+keys — see the Constraints and Relationships references.
+
+**Syntax**
+
+```text
+create table [if not exists] <Name> (<col> <type> [constraints], ...)
+```
+
+## Drop a table
+
+```text
+drop table authors
+```
+
+In advanced mode you may add `if exists` so removing a table that is not
+there succeeds quietly:
+
+```sql
+drop table if exists authors
+```
+
+:::caution
+Dropping a table removes its rows as well. Use `undo` if you drop one by
+mistake.
+:::
+
+## Renaming a table
+
+Renaming a table is available in advanced mode:
+
+```sql
+alter table authors rename to writers
+```
+
+There is no simple-mode rename verb — switch to advanced mode (or use the
+one-line `:` escape) to rename a table.