test(budget): pass selected skills when starting child runners

Fixes #1655.

The budget pause/reserve fixtures call _start_child_runner without the required skills argument added in #1553. On unchanged main (09536cf1), the two affected test modules report 7 failed / 14 passed, all with TypeError: _start_child_runner() missing 1 required keyword-only argument: 'skills'.

Supply skills=[] at the three test call sites. These fake children have no selected skills; the existing budget/pause/reserve assertions now run, and the production signature and skill-specific turn limits remain unchanged.

Validation on macOS, Python 3.12.14, frozen lockfile and isolated HOME/configuration:

• Both affected modules: 21 passed after the change.
• Repository Ruff lint/format and Mypy: passed.
• make check-all reaches the existing repository-wide Pyright failures (941 diagnostics); this test-only patch does not change production code. Bandit was run separately because the aggregate target stops at Pyright.
• git diff --check: passed.

Found while following up on #1654's CI, but kept separate because this is a pre-existing fixture defect. #1577 addresses the other stale runner settings; the provider cost-estimation wait has a separate report. This patch alone does not establish a passing full suite or remote CI. No real LLM, Docker scan or external target was used.

Prepared with Codex assistance.

Combined Linux validation

The complete diagnostic matrix at c0651c343e3d7a58391214a2d6b133b14f363bbe combines #1654, #1657, #1658, #1660 and existing #1577 on current upstream 09536cf1. Python 3.12, 3.13 and 3.14 each pass with 2,534 passed / 3 expected xfails, using the frozen lockfile and normal catalog loading. No tests are skipped.

This validates the fixes together. Each independent PR's own upstream run still inherits the other unresolved base defects; the combined diagnostic does not turn those checks green.