Linked positions (Qualified Start): extra wallets on one account, credits pooled, buy-from picker

- accounts/db: positions table + JSON store (add/list/owner/remove; main-wallet and cross-account guards)
- auth verify: asPosition links a second wallet without touching the session; position wallets can't mint a session
- /api/my/positions (chain-refreshed member ids, buyer counts, credits) + remove
- credits pooled across main + positions on /api/me, dashboard, campaigns; campaign charged to the best-funded position
- My line: own positions listed on level 1 as 'You · position N'
- Buy pane: Qualified Start card + Add a position flow + Buy-from picker with connected-wallet guard
- Wallet pane: Your positions card; chatbot answer updated

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

public/assets/wallet.js

@@ -148,7 +148,7 @@ window.IAPWallet = (function () {
   }
 
   // SIWE: challenge -> personal_sign -> verify (server sets the session cookie)
-  async function signIn() {
+  async function signIn(opts) {
     const addr = await connect();
     const ch = await (await fetch('/api/auth/challenge', { method: 'POST',
       headers: { 'Content-Type': 'application/json' }, body: JSON.stringify({ address: addr }) })).json();
@@ -157,7 +157,7 @@ window.IAPWallet = (function () {
     const hexMsg = '0x' + Array.from(new TextEncoder().encode(ch.message)).map(b => b.toString(16).padStart(2, '0')).join('');
     const sig = await eth().request({ method: 'personal_sign', params: [hexMsg, addr] });
     const r = await (await fetch('/api/auth/verify', { method: 'POST',
-      headers: { 'Content-Type': 'application/json' }, body: JSON.stringify({ address: addr, signature: sig }) })).json();
+      headers: { 'Content-Type': 'application/json' }, body: JSON.stringify({ address: addr, signature: sig, asPosition: !!(opts && opts.asPosition) }) })).json();
     if (r.error) throw new Error(r.error);
     return r;
   }