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.

engine/tests/smoke_test.c

@@ -52,6 +52,14 @@ static void test_natal_sun_sign(void) {
   astro_compute_natal_chart(&birth, &chart);
 
   assert(chart.bodies[PLANET_SUN].sign == SIGN_GEMINI);
+
+  /* Whole-sign house invariant: body.house (1-12) must name the house
+   * whose sign (chart.houses[house-1]) is that same body's sign. */
+  for (int b = 0; b < NUM_BODIES; b++) {
+    assert(chart.bodies[b].house >= 1 && chart.bodies[b].house <= 12);
+    assert(chart.houses[chart.bodies[b].house - 1] == chart.bodies[b].sign);
+  }
+
   printf("PASS test_natal_sun_sign\n");
 }
 
@@ -74,6 +82,12 @@ static void test_reading_generate_smoke(void) {
   for (int b = 0; b < NUM_BODIES; b++) {
     assert(r1.natal.bodies[b].ecliptic_longitude == r2.natal.bodies[b].ecliptic_longitude);
     assert(r1.transits.bodies[b].ecliptic_longitude == r2.transits.bodies[b].ecliptic_longitude);
+
+    /* Transiting planets' houses are read against the natal chart's
+     * houses, not a fresh chart for "now" - same invariant as the natal
+     * bodies, but checked against r1.natal.houses. */
+    assert(r1.transits.bodies[b].house >= 1 && r1.transits.bodies[b].house <= 12);
+    assert(r1.natal.houses[r1.transits.bodies[b].house - 1] == r1.transits.bodies[b].sign);
   }
   assert(r1.transits.aspect_count == r2.transits.aspect_count);