[api] implement invention cheers (#55)

Co-authored-by: Nexi (CWN) <communityshieldofficial@gmail.com>

apps/api/migrations/0018_invention_interaction.sql

@@ -0,0 +1,13 @@
+-- A player's interaction with an invention. One row per (player, invention); `cheered`
+-- is toggled in place and the invention JSON's denormalized `CheerCount` is resynced
+-- after every write. Generated from src/inventions-db.ts (SCHEMA_DDL) — keep in sync.
+
+CREATE TABLE IF NOT EXISTS invention_interaction (
+  player_id INTEGER NOT NULL,
+  invention_id INTEGER NOT NULL,
+  cheered INTEGER NOT NULL DEFAULT 0,
+  created_at TEXT,
+  PRIMARY KEY (player_id, invention_id)
+);
+CREATE INDEX IF NOT EXISTS idx_invention_interaction_invention
+  ON invention_interaction (invention_id);