fix: decay altitude action subtracting altitude when simulation is paused

[SourabhX16]

Problem Statement

decayAltitude interval continues running and updating store altitude even when simulationRunning is false.

Why It Matters

Pausing simulation stops orbit motion but satellite altitude keeps dropping.

Expected Behaviour

decayAltitude action should check simulationRunning flag and abort altitude subtraction when simulation is paused.

Acceptance Criteria

• Satellite altitude decay stops completely when simulation is paused.
• Resumes seamlessly when simulation is unpaused.
• State behavior synchronized.

Likely Affected Files / Components

• src/lib/store.tsx