[Air #641] test: verify SPIR solo mode emits single consultation task

[waleedkadous]

Summary

Adds missing test coverage verifying that porch next respects consultation model configuration — specifically solo mode (single model) and none mode (consultation disabled).

Implements #641

What Changed

Two new tests in next.test.ts:

1. Solo mode test: Mocks loadConfig to return models: ['claude'], asserts porch next emits exactly 1 consultation task containing only claude (not gemini or codex)
2. None mode test: Mocks loadConfig to return models: 'none', asserts porch next emits a "Consultation skipped" task with no consult -m commands

Also refactored the loadConfig mock to use vi.hoisted with a mutable ref (configRef), allowing per-test overrides while keeping the default 3-model behavior for all existing tests. The afterEach resets configRef.models to the default.

Key Decisions

• Used vi.hoisted mutable ref pattern instead of vi.fn().mockReturnValueOnce() because vitest's async mock factories don't properly propagate mockReturnValueOnce overrides to the imported module reference.
• Kept assertions aligned with actual source behavior: solo mode checks N-way consultation subject, none mode checks Consultation skipped subject.

Test Plan

• 2 new unit tests added (solo mode + none mode)
• Build passes (tsc --noEmit)
• All 26 tests in next.test.ts pass
• Full test suite: 2301 passed, 13 skipped, 23 pre-existing failures (unrelated: adopt, consult, update, session-manager)

Review Notes

Net diff is ~45 lines. The configRef approach is minimal and isolated — existing tests are unaffected since afterEach resets to defaults.