Accept pre-parsed JSON body in HttpError.from()

[freshlogic]

Summary

`HttpError.from(response)` now accepts an optional second argument: an already-parsed JSON body. When supplied, the factory skips the body read and sets `err.json` and `err.text` from the supplied value.

This covers the common case of an application-level error envelope on an otherwise-ok response — GraphQL servers (always 200 OK with `data.errors[]`) and some REST APIs (FedEx Rate, etc.) that return 200 with an `errors[]` envelope. The caller has already called `response.json()` to inspect the body and now wants to throw with the body attached.

Before:

```js
const err = new HttpError(res);
err.json = json;
err.text = JSON.stringify(json);
err.message = json.errors.map(e => e.message).join('; ');
throw err;
```

After:

```js
const err = await HttpError.from(res, json);
err.message = json.errors.map(e => e.message).join('; ');
throw err;
```

Design notes

• One factory instead of two — caller doesn't have to choose between `from` and `fromJson`
• Signature stays async (callers were awaiting anyway); no IO when `json` is provided
• No opinion on message format — errors-envelope shapes vary (GraphQL uses `message`; FedEx uses `code`+`message`; JSON:API uses `detail`+`title`+`source`). Callers override `.message` after construction.
• Fully backward compatible — single-arg `from(response)` is unchanged

Test plan

• `from(response, json)` sets `.json`, `.text`, `.cause`, and `.name` correctly
• Caller can override `.message` after construction
• All existing single-arg `from()` tests still pass

🤖 Generated with Claude Code

[coveralls]

Coverage Report for CI Build 25706064232

Coverage remained the same at 100.0%

Details

• Coverage remained the same as the base build.
• Patch coverage: 12 of 12 lines across 1 file are fully covered (100%).
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	46
Covered Lines:	46
Line Coverage:	100.0%
Relevant Branches:	8
Covered Branches:	8
Branch Coverage:	100.0%
Branches in Coverage %:	Yes
Coverage Strength:	2.57 hits per line

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💛 - Coveralls

[freshlogic]

Closing — went with the clone-before-consume pattern on the caller side instead, no http-error change needed.