fix(cli): name the network cause of a failed fetch in the error box - #7236

Approving at 081637f0.

Checked:

• Fails without the fix: I put errors.ts back to the main version (b7a8cfa7) and the named test fails: names the network cause of a failed fetch on the third line, and nothing for a free-text cause is missing the expected "code: ETIMEDOUT" third line. With the fix, all 14 tests in errors.test.ts pass.
• Message line unchanged: the second argument to errorBox is still err.message (fetch failed). recordFailure(title, hint ?? suggestion) records that same message, so anything matching on it sees no change. The cause shows up only in the suggestion slot, and only when the caller passed no suggestion.
• Scope: only the generic Error branch changes. HyperframesApiError and non-Error values behave as before. The ^[A-Z][A-Z0-9_]{2,40}$ check keeps free-text or path-like cause.code values out of the output.
• Types: tsc shows no errors in cloud/errors.ts. CI passed on this head.

Nit (not blocking): networkCode and its one-line doc sit between reportApiError's long JSDoc block and the function itself. That JSDoc now attaches to networkCode, so reportApiError loses its hover docs. Moving networkCode above that block would fix it.