feat(highscore-server): store a crazy-mode flag per score

The game is getting a crazy mode that drops extra balls, and scores
reached with it should still enter the shared table but be visibly
labelled. The service therefore has to persist and return that label.

API:
- POST /api/highscores accepts an optional "crazy" boolean. Missing
  means false, so cached clients from before crazy mode keep working.
- GET responses include "crazy" on every entry. Older clients ignore
  unknown fields (serde default behaviour), so the new response shape is
  safe for them too.

Database:
- New databases get a `crazy INTEGER NOT NULL DEFAULT 0 CHECK (crazy IN
  (0, 1))` column.
- Existing databases are migrated on open: if pragma_table_info shows no
  `crazy` column, ALTER TABLE adds it with the same definition. SQLite
  fills existing rows with the default, so every historic score stays a
  normal score. No data is rewritten and the migration is idempotent.

Ordering and the top-ten pruning are unchanged; the flag is not part of
the ranking.

Test Plan:
- cargo test --manifest-path highscore-server/Cargo.toml
  - pre_crazy_mode_database_is_migrated_in_place: builds the old schema
    with a row, opens it, submits a crazy score, checks both rows come
    back with the right flag, and reopens the migrated file.
  - api_accepts_crazy_flag_and_defaults_it_for_old_clients: one request
    without the field, one with "crazy": true.
- Deploy: restart the service against the production database and check
  GET /api/highscores lists the old entries with "crazy": false.

tdkpin-rs/highscore-server/README.md

@@ -8,8 +8,12 @@ GET  /api/highscores
 POST /api/highscores
 ```
 
-The POST body is JSON with a 21-character maximum name and a `u32` score. The
-response is the canonical top-ten JSON array.
+The POST body is JSON with a 21-character maximum name, a `u32` score, and an
+optional `crazy` boolean (default `false`) marking a crazy-mode score. The
+response is the canonical top-ten JSON array, each entry carrying `crazy`.
+
+Databases created before crazy mode gain the `crazy` column automatically on
+startup; existing rows become normal scores.
 
 A newly created database starts with the original distributed demo table. An
 existing database, including an existing empty database, is left unchanged.