Replace hover-based aircraft movement with a two-state system: LANDED
(grounded, cannot shoot, vulnerable to all weapons) and FLYING (at
cruise speed, uses air domain protection). Aircraft can no longer stop
in mid-air; armed units execute strafing passes with overshoot and
come-about logic.
Key changes:
- Add `liftFrac` simulation state for altitude, `airborne` dynamic flag
(vs static `isAir`) so landed aircraft are ordinary ground targets
- Implement `stepStraferOrders` for aircraft that overfly targets and
repeat passes; idle aircraft clear hostile keepout zones
- Add `overshoot` and `keepout` flight properties to fighter/bomber
- AI gains static defense (Laser Tower, Missile Launcher) at skill 4+,
with threat-based placement and economy gating
- Fighter gains ground gun (pintlegun); air management uses `airClaimed`
set instead of interceptor-only classification
- Update campaign m05 seed (71644) to compensate for balance shifts
- Update tooltips, documentation, and tests for new behavior
Closes#1234