fix(sdk): handle non-JSON success response for streak freeze buy

[sentry]

This PR addresses a SyntaxError: JSON.parse: unexpected character that occurred when the /private-api/streak-freeze/buy endpoint returned a successful (2xx) HTTP response with a non-JSON body (e.g., empty or HTML).

Root Cause:
The buyStreakFreezeRequest function in packages/sdk/src/modules/quests/mutations/buy-streak-freeze.ts was calling response.json() directly on the success path without checking the Content-Type header or wrapping it in a try/catch block. This led to an unhandled SyntaxError if the server responded with valid HTTP status but an unexpected body format.

Solution:
Implemented a more robust response parsing mechanism, mirroring the approach already present in use-claim-points.ts:

1. The response body is now initially read as plain text using response.text().
2. The Content-Type header is checked. If it does not indicate JSON, a descriptive error ([SDK][StreakFreeze] – expected JSON but received "..." response) is thrown.
3. If the Content-Type is JSON, JSON.parse() is called within a try/catch block. If parsing fails, a descriptive error ([SDK][StreakFreeze] – malformed JSON response) is thrown.

This ensures that unexpected response formats are handled gracefully, preventing unhandled SyntaxError exceptions and providing clearer error messages for debugging.

Test Updates:

• Updated existing fetch mocks in buy-streak-freeze.spec.ts to include headers.get() and text() methods, as the new implementation relies on these.
• Added new test cases to specifically cover scenarios where the API returns a 2xx response with a non-JSON Content-Type or malformed JSON.

Fixes ECENCY-NEXT-1FCJ

_{This PR was automatically generated by Sentry. You can adjust this setting at any time.}

[feruzm]

Closing: the issue is real but this is not the code that throws it.

ECENCY-NEXT-1FCJ is an unhandled rejection on /perks in all 11 retained events. buy-streak-freeze.ts cannot be its source:

1. The file landed on 2026-07-06, while 6 of the 11 events predate it (2026-05-22 through 2026-07-02).
2. Its only call site, handleBuyFreeze in apps/web/src/app/perks/components/perks-quests-section.tsx, already wraps await buyFreeze() in try/catch, so a SyntaxError there could never surface as an unhandled rejection.
3. No event's breadcrumbs contain a /private-api/streak-freeze/buy request.
4. The 2026-07-10 event's last breadcrumb before the throw is POST 502 /private-api/post-game, and the 2026-07-26 event ends with clicks on the spin modal's body and footer.

The actual source is game-claim.ts, which calls response.json() with no ok check and no content-type check, reached from an uncaught await claim() in perks-points-spin-banner.tsx. Fixed in #1526, which uses the same content-type guard this PR proposed.

Worth noting the same issue ID was already "fixed" once in use-claim-points.ts on 2026-07-10 and kept firing afterwards, for the same reason: the file was guessed from the pattern rather than from the event trail.