[econ] mostly working challenges

apps/econ/migrations/0011_challenge_gift.sql

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+-- Weekly-challenge gift grants, owned by the `econ` worker. One row per (account,
+-- rotation), written when the last challenge of a rotation is reported complete on
+-- `/api/challenge/v2/updateProgress` and the rotation's `Gift` is handed out.
+--
+-- The table exists only to make that grant happen ONCE. The client reports progress
+-- repeatedly, so every report that arrives with the set already finished would otherwise
+-- mint another copy of the reward; the insert is the gate, and it conflicts on the second
+-- report instead of paying out again.
+--
+-- Keyed by rotation as well as account so a new week's set can be finished and rewarded on
+-- its own — `challenge_map_id` is the rotation, matching `challenge_status`. There is no
+-- `granted` flag: the row's existence IS the grant. Kept in sync with
+-- CHALLENGE_GIFT_SCHEMA_DDL in src/challenge-db.ts.
+
+CREATE TABLE IF NOT EXISTS challenge_gift (
+  account_id INTEGER NOT NULL,
+  challenge_map_id INTEGER NOT NULL,
+  granted_at TEXT NOT NULL,
+  PRIMARY KEY (account_id, challenge_map_id)
+  );