fix(test): reject whitespace-only --name in test update (parity with test create)

[lxcario]

What

test update --name " " (whitespace-only) is accepted and would send a blank name to the backend, while the sibling test create --name " " correctly rejects it with VALIDATION_ERROR (exit 5).

Why this matters

A whitespace-only name produces a junk test record that is effectively invisible in test list output and the dashboard. The test create path already prevents this via requireString (dogfood P1 fix #1); test update missed the same guard and only checks the upper length bound.

Reproduction

# test update -- whitespace name ACCEPTED (exit 0), would send "   " to backend:
$ testsprite test update test_abc --name "   " --dry-run --output json
{ "testId": "test_dryrun_update_2026", "updatedFields": ["name"], ... }   # exit 0

# control: test create -- whitespace name correctly REJECTED (exit 5):
$ testsprite test create --project proj_1 --type frontend --name "   " --code-file x.ts --dry-run --output json
{ "error": { "code": "VALIDATION_ERROR", "nextAction": "Flag `--name` is invalid: is required." } }   # exit 5

Root cause

src/commands/test.ts, runUpdate (line ~1212). The function validates name length:

if (opts.name !== undefined && opts.name.length > 200) {
  throw localValidationError('name', 'must be at most 200 characters');
}

But has no lower-bound / whitespace check. A whitespace-only string passes opts.name !== undefined (it's a non-empty string), the length check (3 < 200), and flows into the PATCH body.

Fix

Add a whitespace rejection before the length check, mirroring the existing requireNonEmpty / requireString pattern used elsewhere in the same file:

if (opts.name !== undefined && opts.name.trim().length === 0) {
  throw localValidationError('name', 'must be a non-empty string (whitespace-only is not allowed)');
}

Tests

Added 1 regression test to src/commands/test.test.ts (in the runUpdate describe block) asserting name: ' ' rejects with VALIDATION_ERROR / field name and makes no network call. Fails on main before this fix; passes after.

• Before (main): Tests 16 failed | 1359 passed | 72 skipped
• After (this branch): Tests 16 failed | 1360 passed | 72 skipped (+1 new test)

The 16 failures are pre-existing and environment-specific (Windows path/line-ending), unrelated -- see #4.

Verification

• npm test: same 16 pre-existing (environment-specific) failures as baseline, zero new
• npm run typecheck: pass
• npm run lint: pass