Add unit tests for InterMission and Help modules (94 new tests)

[Copilot]

Command-level tests are complete (188 commands covered, 7205 tests passing). This PR moves to the next coverage phase: previously-untested core modules.

InterMission (25 tests)

• RankUpCost: All three upgrade cost modes (standard 10-step, low-cost, 15-step) with full rank sweep, separation/main-form restrictions, time limits, cost modifier feature, and disable guard
• MaxRank: Default/5-step/15-step options, Disable(unit,改造) global variable guard, 最大改造数 feature cap

// Example: verifies all 10 standard-mode rank costs in one pass
var expected = new[] { 10000, 15000, 20000, 40000, 80000, 150000, 200000, 300000, 400000, 500000 };
for (int rank = 0; rank < expected.Length; rank++)
{
    var src = CreateSrc();
    var unit = CreateUnit(src, "全ランク機" + rank, rank);
    var im = new InterMission(src);
    Assert.AreEqual(expected[rank], im.RankUpCost(unit));
}

Help.AttributeName (69 tests)

• Full branch coverage of the weapon-attribute-code → display-name mapping (~60 attribute codes)
• is_ability parameter branching for 共 and 音 attributes

Results

• 7205 → 7299 tests, 0 failures, no regressions
• Status.cs (5,355 lines) confirmed entirely commented-out (unported VB6) — not testable yet