reliability: SimpleFin API calls don't validate HTTP response status

[moltboie]

Problem

getData() in src/server/lib/simple-fin/data.ts and exchangeSetupToken() in tokens.ts call fetch() but never check response.ok or response.status.

data.ts (line ~37)

const response = await fetch(`${url}/accounts?${params.toString()}`, {
  headers: { Authorization: `Basic ${credentials}` },
});
// No status check!
const data: ResponseData = await response.json();

tokens.ts (line ~22)

const response = await fetch(setupUrl, { method: "POST", headers: { "Content-Length": "0" } });
// No status check!
return await response.text();

Impact

• A 4xx/5xx response will either throw on .json() (returning HTML error page) or return an error payload that gets treated as valid account data
• exchangeSetupToken could return an error page body as the access URL, causing cryptic failures later
• Compare with polygon.ts which properly checks response.ok and returns typed PolygonResult

Fix

Add response.ok checks and return meaningful errors, matching the pattern already used in polygon.ts:

if (!response.ok) {
  throw new Error(`SimpleFin API error: ${response.status} ${response.statusText}`);
}

Also validate the response shape before passing to modelize() (e.g. check data.accounts is an array).