Reject work intents without energy

[junaga]

Fixes #151.

What changed

• Require a strictly positive energy amount before processing build, repair, or controller-upgrade intents.
• Add regression coverage for an empty creep store in all three work-intent handlers.

Why

undefined <= 0 is false in JavaScript. When a creep's store lacks an energy property, the existing guards therefore let the intent continue and arithmetic propagates NaN into creep, target, stats, and event data.

The positive-value check rejects zero, missing, and invalid energy values before any state is changed.

Validation

• Full Jasmine suite: 111 specs, 0 failures
• Gulp build completed successfully