fix(teams): make "replace the whole set" actually replace it

Found walking the live rig, which is the only place it could be found: every unit
test and the settings screen itself send every row, so the bug was invisible to
both.

`PUT /auth/me/notifications/teams` documents itself as replacing the whole set. It
did not — it wrote the entries it was given and left every other preference
standing. So `{"teams": []}` cleared nothing, which is precisely the body the route
requires the array for: the field is mandatory even when empty so that clearing
everything is expressible, and it was the one thing that did not work.

A Team the caller could have named and did not now returns to its defaults. RESET
rather than deleted, and the difference is `last_digest_at`: that column is the
digest worker's state and not a preference, so dropping the row with it would make
every visit to the settings screen re-open a day-wide digest window and mail
somebody a summary they had already read.

Walked again after the fix on the real database: the empty set clears, an entry
naming a Team the caller is not in is still dropped, and the digest stamp survives.

Co-Authored-By: Claude <noreply@anthropic.com>

server/src/model/teams/teamNotify.model.js

@@ -82,6 +82,24 @@ async function replacePrefs(userId, entries) {
     await db.setPref(userId, teamId, { muted: Boolean(entry.muted), emailMode })
     written.push(teamId)
   }
+
+  // A Team the caller COULD have named and did not is returned to its defaults.
+  //
+  // Without this, "replace the whole set" was a lie the endpoint told: omitting an
+  // entry left the old preference standing, which made `teams: []` — the body the
+  // route requires precisely so that clearing everything is expressible — clear
+  // nothing at all.
+  //
+  // Reset rather than deleted, and the difference is `last_digest_at`. That column
+  // is the digest worker's state, not a preference; dropping the row with it would
+  // make every visit to the settings screen re-open a day-wide digest window and
+  // mail somebody a summary they already read.
+  for (const teamId of allowed.keys()) {
+    if (written.includes(teamId)) continue
+    // eslint-disable-next-line no-await-in-loop
+    await db.setPref(userId, teamId, { muted: false, emailMode: 'off' })
+  }
+
   return { written, prefs: await listPrefs(userId) }
 }