Docs: the database through SeaORM

CLAUDE.md and the architecture notes described the SQL schema and migrate(),
both gone: the entities are the schema, create_missing makes what is missing,
and hand-written SQL has to run on SQLite and Postgres both.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CLAUDE.md

@@ -125,7 +125,7 @@ Non-trivial logic leaves one runnable check behind. Pure functions (`merge_polic
   subscriber. Two feeds publishing the same URL means only the first one scanned shows it.
 * **Read state lives in `entry_state`, per user, and nowhere else.** `entries` had `read`, `flagged`
   and `position` columns from before accounts; two bugs came from queries still reading them
-  (retention, and the entry pruner), and `migrate()` now drops them.
+  (retention, and the entry pruner), and they were dropped in 0.5.
 * **The catalogue is config.toml; the subscriptions are in the database.** A feed exists once;
   `subscriptions(user_id, feed_id)` says who wants it and with what settings. OPML children are
   derived and never written to config.
@@ -140,10 +140,16 @@ Non-trivial logic leaves one runnable check behind. Pure functions (`merge_polic
 * `/api/settings` answering `200` does **not** mean the daemon is well — the web server is a
   different task. `ipx status` checks the control socket and the database; to see the worker
   getting through its jobs, watch for `scan complete` in the log.
-* **Every `ipx` command runs `migrate()` when it opens the database**, the healthcheck's
-  `ipx status` included. A migration that rewrites a big table (`DROP COLUMN`) takes seconds on
-  production, and a command run meanwhile fails with `migrating schema`. It changes nothing; wait
-  for `daemon started` in the log. Copy `state.db` aside before deploying one.
+* **The database goes through SeaORM, and the entities in `src/entity.rs` are the schema.**
+  `Db::open` creates any missing table or index from them (`create_missing`), on every `ipx`
+  command, the healthcheck's `ipx status` included, so it must never write when nothing is
+  missing: SeaORM's experimental schema sync dropped and remade an index on every open, the
+  write lock that took made `ipx status` time out behind a busy daemon, and it was removed for
+  it. A new column on an existing table needs its own `ALTER`; nothing adds one for you.
+* **SQL written by hand in `db.rs` has to run on SQLite and Postgres both** (issue #18): `$1`
+  parameters, bound only if used; `ON CONFLICT`, not `INSERT OR IGNORE`; yes/no columns tested
+  as themselves (`NOT coalesce(s.read, false)`) and written as `true`/`false`, never compared to
+  1; no `rowid`, `GLOB` or `UPDATE OR IGNORE`. `Args` in `db.rs` builds the parameters.
 
 ## House style