Annual stellar aberration (~20 arcsec) added to all 6 existing _apparent()
functions via classical first-order v/c projection (Ron & Vondrak). Earth
velocity sourced from VSOP87 xyz[3..5] (analytic) or DE numerical
differentiation.
New functions (106 -> 114):
- eq_angular_distance(): Vincenty formula, stable at 0 and 180 deg
- eq_within_cone(): cosine shortcut for fast cone-search predicate
- <-> operator on equatorial type
- 6 DE apparent variants with VSOP87 fallback:
planet/sun/moon_observe_apparent_de(),
planet/moon_equatorial_apparent_de(),
small_body_observe_apparent_de()
Stellar parallax now functional in star_observe_pm() and
star_equatorial_pm() — Green (1985) Eq. 11.3 displacement using
Earth heliocentric position from VSOP87.
All 19 regression suites pass (18 existing + new aberration suite).
