Added CLAUDE.md and development rules for Claude Code.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

.claude/rules/database.md

@@ -0,0 +1,15 @@
+---
+paths:
+  - "migrations/**"
+  - "src/backend/data.rs"
+---
+
+# Database rules
+
+- PostgreSQL. Schema changes are plain SQL files in `migrations/`, named `NN_short_name.sql` with the next two-digit number. They are embedded with `sqlx::migrate!()` and applied automatically at server start.
+- Never edit or rename a migration that has been committed — sqlx stores a checksum per version and existing installations will refuse to start. Fix things with a new migration.
+- Migrations must work on a database that already holds production data: add columns as nullable or with a `DEFAULT`, backfill in the same file if needed.
+- `migrate!()` reads the directory at compile time and there is no `build.rs`, so cargo may not notice a new `.sql` file. If a new migration doesn't run, touch `src/main.rs` and rebuild.
+- Default rows (admin user, company, message templates, appearance) are seeded in Rust at startup (`create_admin`, `check_*`), not in migrations. A new singleton table or `message_type` value needs the matching seeding code.
+- Keep the schema and `src/backend/data.rs` in sync in the same change: column names = struct field names (`SELECT *` + `FromRow`), Postgres enum labels = Rust variant names. A new enum value needs `ALTER TYPE ... ADD VALUE` plus the Rust variant, its `Display` arm and, for `message_type`, the list in `check_messages`.
+- Naming: singular snake_case tables (`reservation_sum`, `closing_time`), `id SERIAL PRIMARY KEY`, `"user"` always quoted, money as `NUMERIC(9, 2)` ↔ `rust_decimal::Decimal`, dates/times as `DATE`/`TIME` ↔ `chrono::NaiveDate`/`NaiveTime`.