feat(rewards): add game points endpoint with reason codes

Frontend shows why a game earned no points after a status save.
Settle runs first. Rules and amounts are not changed.

readme.md

@@ -103,6 +103,7 @@ flowchart LR
     Facts["counted_user_game + playtime days + status log + time to beat + user_game_question"] --> Rule["OpenQuestion.of"]
     Rule --> Card["question card"]
     Answer["answer"] --> Backlog["BacklogService"] --> UserGame["user_game"] --> Trigger["V14 trigger: status log"] --> Settle["RewardService.settle"]
+    Answer -->|"Frontend: GET /api/rewards/games/{appid}"| Settle
     Answer -->|no| Snooze["user_game_question"]
 ```
 - **Hide games**: a user can hide a game, Steam or added by hand (e.g. a playtest or a tool). It leaves every list and number: library,
@@ -132,11 +133,11 @@ flowchart LR
   (old and new status, time, whether the user chose it), whatever code path made it. It starts with V14; older
   changes are not known.
 - **Pile Points** (`modules/rewards`): users earn points for playing games off the pile, in an append-only ledger
-  (`reward_ledger`, V26; the balance is the sum). No code path pays: a settle (on `GET /api/rewards/wallet` and
+  (`reward_ledger`, V26; the balance is the sum). No code path pays: a settle (on `GET /api/rewards/wallet`, on `GET /api/rewards/games/{appid}` and
   nightly at 02:30, `app.rewards.settle-cron`) derives rows from the status log, playtime days, achievements and pile
   snapshots, once per user, kind and game (`ref`). Rules and numbers: `RewardRules`; a Steam finish needs playtime and one
   proof of fresh play (ending achievement or playtime around the finish, or half of the IGDB time played since the finish; old history pays nothing). The month bonus needs a finished game in that month. Games added by hand pay 15 for
-  a finish, at most 3 per ISO week. The settle takes a per-user advisory lock. V26 also pays a one-time starter grant
+  a finish, at most 3 per ISO week. `GET /api/rewards/games/{appid}` (game page open, after every status save) settles, then answers the paid rows of the game and its set (`bookedNow` = written by this call) and one `NoPointsReason` per missing kind (`STARTED`, `FINISHED`, `COMPLETED`); the codes live in `RewardRules`, the Frontend only maps them to texts. The settle takes a per-user advisory lock. V26 also pays a one-time starter grant
   for finishes from before the status log. Shop: a whitelist of 57 looks (`ShopItem`; 45 buyable and 12 unlock-only) in eight slots, including animated completed effects, page backgrounds (CSS, SVG and two canvas engines in the Frontend),
   banner backgrounds (V27 widens `reward_equipped.slot`) and three buyable skins (full themes, slot `SKIN`). The unlock-only
   items (price 0, never sold): the settle books an `UNLOCK` row (ref = item code, 0 points) once a