FlightGear - Flight Simulator FGAddon

- SFOM 83A gunsight: replace path-drawn reticle with image-based reticle (SFOM_83A_03_Cross_1024.png), render canvas onto the collimator glass object instead of separate vtm object, make canvas background transparent, and centre reticle by default; remove obsolete vtm.ac, vtm.png, vtm.xml
- Aerodynamics: increase pitch damping, elevator authority, and alpha-dot coefficients; reduce pitch gain from 1.3 to 0.95
- Add dorsal fin model (dorsal_fin.ac) with livery texture support
- Update frontal landing gear door animation sequencing
- Remove non-functional canopy toggle key binding (C)