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.

docs/input-output-format.md

@@ -91,10 +91,13 @@ typedef struct {
 ```
 
 - **`NatalChart`** (`astro.h`): `bodies[10]` (Sun..Pluto, each a sign +
-  degree-in-sign + raw ecliptic longitude), `ascendant_longitude`,
-  `houses[12]` (whole-sign: `houses[0]` is the Ascendant's sign).
+  degree-in-sign + raw ecliptic longitude + whole-sign `house` 1-12),
+  `ascendant_longitude`, `houses[12]` (whole-sign: `houses[0]` is the
+  Ascendant's sign).
 - **`DailyTransits`** (`astro.h`): `bodies[10]` (today's positions, same
-  shape as above), `moon_phase` (one of 8 named phases), `aspects[]` +
+  shape as above — `house` here is the natal chart's house the
+  transiting planet currently occupies, not a fresh "houses for right
+  now" chart), `moon_phase` (one of 8 named phases), `aspects[]` +
   `aspect_count` (each aspect names a transiting planet, a natal planet,
   an `AspectType` — conjunction/sextile/square/trine/opposition — and
   the orb in degrees).
@@ -107,22 +110,22 @@ typedef struct {
 ### `--format text`
 
 Four `=====`-delimited sections, in order: natal chart (each body's sign
-+ degree, then the Ascendant), today's sky (Moon phase, then each body's
-transiting position), today's aspects to the natal chart (one line per
-aspect, with orb), and the Celtic Cross (one block per position: name,
-card, `(Reversed)` if applicable, the position's meaning, then the
-card's meaning).
++ degree + house, then the Ascendant), today's sky (Moon phase, then each
+body's transiting position + the natal house it currently occupies),
+today's aspects to the natal chart (one line per aspect, with orb), and
+the Celtic Cross (one block per position: name, card, `(Reversed)` if
+applicable, the position's meaning, then the card's meaning).
 
 ```
 ===== Natal Chart =====
-Sun       23.5° Taurus
-Moon      15.2° Capricorn
+Sun       23.5° Taurus      (House 3)
+Moon      15.2° Capricorn   (House 11)
 ...
 Ascendant  18.4° Pisces
 
 ===== Today's Sky =====
 Moon phase: Waning Gibbous
-Sun       11.5° Cancer
+Sun       11.5° Cancer      (House 5)
 ...
 
 ===== Today's Aspects to Natal Chart =====