Add astrological houses to natal chart and daily transits

Every planet position now carries its whole-sign house (1-12); transits
report the natal house each transiting planet currently occupies rather
than a fresh "houses for right now" chart, matching how transits are
normally read. Surfaced in both text and HTML output, fully translated.

CLAUDE.md

@@ -120,6 +120,13 @@ you touch this function, keep the intermediate type 64-bit.
   Engine has no Ascendant function; it's computed directly in `astro.c`
   from sidereal time + a standard low-precision obliquity polynomial +
   the RAMC/obliquity/latitude identity (Duffett-Smith & Zwart).
+- Every `PlanetPosition` (`astro.h`) carries a whole-sign `house` (1-12),
+  via `assign_houses()`/`whole_sign_house()`. **`DailyTransits.bodies[*].house`
+  is always relative to the *natal* Ascendant**, not a fresh "houses for
+  right now" chart — that's the standard, personalized way transits are
+  read (e.g. "transiting Jupiter is in your 5th house"), and it's why
+  `astro_compute_daily_transits` takes the natal chart as a parameter in
+  the first place (also used for aspect detection).
 - Aspects (conjunction/sextile/square/trine/opposition) use an 8° orb
   when a luminary (Sun/Moon) is involved, 6° otherwise.