fix(google-health): store the account's id, not the word "profile"

The profile's resource name is `users/{user}/profile`, and the connect
stored its last segment, the same constant for every account. Since the
one-account-per-record check, a second record on an instance could not
connect or reconnect Google Health: it was refused as `already_linked`.

The connect now stores the `{user}` segment, reads `users/me/identity`
when the profile answers through the `me` alias, and stores the id as
unknown when neither names the account. A migration makes the column
nullable and clears the placeholder, so the next connect stores the
real id.

prisma/migrations/0491_google_health_user_id_repair/migration.sql

@@ -0,0 +1,30 @@
+-- Google Health user id repair.
+--
+-- `google_health_connections.google_user_id` held the last path segment of
+-- the profile's resource name `users/{user}/profile`, which is the constant
+-- `profile` for every account. Since the one-account-per-record check every
+-- connection therefore looked like the same Google account, and a second
+-- record on the instance could not connect or reconnect (`already_linked`).
+--
+-- The column becomes nullable (null = id unknown, which the check treats as
+-- no evidence of a second holder) and the placeholder values are cleared. The
+-- next connect of each record stores the real id. The table holds one row per
+-- connected record, so the update is small; the lock wait is bounded.
+--
+-- Reversibility: the cleared values were the same constant on every row and
+-- identified nothing; restoring NOT NULL needs a value on every row first.
+--
+-- Both statements are repeatable, so a run stopped by the lock timeout is
+-- safe to retry.
+-- @retry-on-lock-timeout
+
+DO $migration$
+BEGIN
+    PERFORM set_config('lock_timeout', '5s', true);
+    ALTER TABLE "google_health_connections"
+        ALTER COLUMN "google_user_id" DROP NOT NULL;
+    UPDATE "google_health_connections"
+    SET "google_user_id" = NULL
+    WHERE "google_user_id" IN ('profile', 'me', '');
+END
+$migration$;

prisma/schema.prisma

@@ -4614,7 +4614,7 @@ model FitbitOAuthState {
 model GoogleHealthConnection {
   id                  String    @id @default(cuid())
   userId              String    @unique @map("user_id")
-  googleUserId        String    @map("google_user_id") // Google external account id
+  googleUserId        String?   @map("google_user_id") // Google Health user id; null when the connect could not read it
   accessToken         String    @map("access_token") // encrypted at app level
   refreshToken        String    @map("refresh_token") // encrypted at app level
   tokenExpiresAt      DateTime  @map("token_expires_at")