#2933 fix(cli): keep TUS upload failure detail instead of "unknown error"

Summary

• A failed capgo bundle upload with an empty response body reached the user as the literal string unknown error — the HTTP status, request URL, and raw body were all dropped. This minted a fresh error tracking issue per occurrence and left both the user and the team unable to act.
• Root cause: the uploadTUS onError handler ran JSON.parse outside any try/catch and rejected a bare string, so an empty body collapsed to unknown error and a non-JSON proxy page (HTML 502/504) threw a SyntaxError inside the tus callback.
• Fix: port the handler shape that already works in cli/src/build/request.ts — wrap the parse in a try/catch that falls back to the raw body then the tus error message, add the HTTP status and request URL to the message, and reject a real Error.

Case	Before	After
Empty body	unknown error	TUS upload failed (status 502, url …): <body or tus message>
Non-JSON body (HTML 502/504)	SyntaxError thrown in callback	raw body surfaced in a rejected Error
JSON body (invalid_apikey, app_not_found, …)	real cause (unchanged)	real cause (unchanged)

Test plan

• No behaviour change for the JSON-body path (invalid_apikey, app_not_found, insufficient_permissions) — those still surface their real cause.
• Empty-body and non-JSON-body failures now reject a real Error carrying the status, URL, and body instead of unknown error.

Screenshots

Checklist

• My code follows the code style of this project and passes
  bun run lint:backend && bun run lint.
• My change requires a change to the documentation.
• I have updated the documentation
  accordingly.
• My change has adequate E2E test coverage.
• I have tested my code manually, and I have provided steps how to reproduce
  my tests

Agent context

• Complementary to open PR #2932, which also touches cli/src/utils.ts but fixes the neighbouring $exception_fingerprint problem in findSavedKey; it leaves the uploadTUS handler alone, so the two do not conflict.

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