[www] password/email recovery (#146)

* pw/email recovery

* fix migration

apps/auth/migrations/0013_account_email_unique.sql

@@ -0,0 +1,44 @@
+-- An email address belongs to ONE account. Password recovery (`auth`
+-- `POST /account/recoverpassword`) is handed nothing but the address the player typed and
+-- has to find their account from it, which only works if no two accounts share one.
+--
+-- Exposed as a generated column, case-folded, with an empty or absent email read as NULL so
+-- accounts without one never collide — and a UNIQUE partial index over it, which is what
+-- actually refuses a second holder. `accounts` `POST /account/me/email` checks first and
+-- answers a refusal the player can read; the index is the backstop against a race.
+--
+-- Before the index can be built, existing duplicates have to go: the LOWEST account id
+-- keeps the address (the first account to claim it) and the others lose theirs, since a
+-- recovery sent to a shared address could only ever reach one of them anyway. Those
+-- players set it again from the account page or in game.
+--
+-- The clean-up runs over a throwaway plain index on the column. Without one, finding each
+-- address's keeper is a scan of the whole table — parsing every row's JSON — PER ROW with
+-- an address, which is what a correlated `MIN(account_id)` did on the first attempt and
+-- what D1 killed for exceeding its CPU limit. With it, the duplicates are one grouped
+-- index walk and the update one indexed join.
+--
+-- Kept in sync with SCHEMA_DDL in @repo/domain's accounts-db.ts (and its mirror in
+-- apps/econ/src/avatar-db.ts).
+
+ALTER TABLE account ADD COLUMN email_lower TEXT GENERATED ALWAYS AS (NULLIF(lower(json_extract(data, '$.email')), '')) VIRTUAL;
+
+CREATE INDEX idx_account_email_lower_dedupe ON account (email_lower) WHERE email_lower IS NOT NULL;
+
+UPDATE account SET data = json_remove(data, '$.email')
+ WHERE account_id IN (
+   SELECT a.account_id
+     FROM account a
+     JOIN (
+       SELECT email_lower, MIN(account_id) AS keeper
+         FROM account
+        WHERE email_lower IS NOT NULL
+        GROUP BY email_lower
+       HAVING COUNT(*) > 1
+     ) d ON a.email_lower = d.email_lower
+    WHERE a.account_id > d.keeper
+ );
+
+DROP INDEX idx_account_email_lower_dedupe;
+
+CREATE UNIQUE INDEX IF NOT EXISTS idx_account_email_lower ON account (email_lower) WHERE email_lower IS NOT NULL;