What Propulsion is — burns, Δv budget, tanks, engines

Propulsion is the spacecraft propulsion-management module: plan burns, execute them, track tank state, monitor engine health, and watch the live Δv budget.

Tabs (with the live Δv budget pinned ABOVE the tab bar so it's always visible):
• **Burn Plans** — proposed and approved future burns.
• **Executed Burns** — past burns with measured performance.
• **Engines** — engine registry: type, thrust, Isp, cycles, condition.
• **Tanks** — propellant tank levels: fuel, oxidizer, pressurant. Mass and pressure.
• **Abort Modes** — contingency burn profiles (deorbit, free-return, contingency rendezvous).
• **Alarms** — open alarms: thrust anomaly, tank pressure, ullage, ignition failure.

Δv budget tracker (always visible):
- **Budget** — total mission-allocated Δv
- **Expended** — sum of executed burns (Tsiolkovsky)
- **Reserved for aborts** — sum of feasible aborts at current state
- **Available** — budget minus expended minus reserved

When you log a burn, Tsiolkovsky computes the actual Δv from start-mass + propellant-burned + Isp, decrements tanks by the engine's mixture ratio, and bumps engine cycles by 1.