Referral purchase email names the buyer: @username in subject and body

memberLabel() resolves @username, or the owner's username for a linked
position, else member #id. Subject: '@name just bought a $20 ad package'.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

accounts.js

@@ -194,6 +194,7 @@ const J = {
   },
   async setPositionMember(a, id) { const p = this.db.positions[a]; if (p && p.memberId !== id) { p.memberId = id; this.save(); } },
   async positionOwner(a) { const p = this.db.positions[a]; return p ? { address: a, email: p.email, memberId: p.memberId || 0 } : null; },
+  async positionByMember(id) { const e = Object.entries(this.db.positions).find(([, p]) => p.memberId === Number(id)); return e ? { address: e[0], email: e[1].email, memberId: e[1].memberId } : null; },
   async removePosition(e, a) {
     const p = this.db.positions[a];
     if (!p || p.email !== e) return { error: 'No such position.' };
@@ -342,6 +343,7 @@ const D = {
     const r = (await db.q('SELECT * FROM positions WHERE address=?', [a]))[0];
     return r ? { address: r.address, email: r.email, memberId: r.member_id || 0 } : null;
   },
+  async positionByMember(id) { const r = await db.q('SELECT address, email, member_id FROM positions WHERE member_id=? LIMIT 1', [Number(id)]); return r[0] ? { address: r[0].address, email: r[0].email, memberId: r[0].member_id } : null; },
   async removePosition(e, a) {
     const r = (await db.q('SELECT * FROM positions WHERE address=? AND email=?', [a, e]))[0];
     if (!r) return { error: 'No such position.' };
@@ -452,5 +454,6 @@ module.exports = { init, signup, login, ensure, byEmail, byAddress, byCode, byUs
   addPosition: (e, a) => { const x = normAddr(a); return /^0x[0-9a-f]{40}$/.test(x) ? impl().addPosition(normEmail(e), x) : Promise.resolve({ error: 'Bad wallet address.' }); },
   setPositionMember: (a, id) => impl().setPositionMember(normAddr(a), Number(id) || 0),
   positionOwner: a => impl().positionOwner(normAddr(a)),
+  positionByMember: id => impl().positionByMember(Number(id) || 0),
   removePosition: (e, a) => impl().removePosition(normEmail(e), normAddr(a)),
   byMemberId: id => impl().byMemberId(id) };