Add narrative text and a day-significance rank to the interpreter

Each of the day's top significant transits now gets a short sentence
describing what it classically means and which area of life its house
governs, condensed from Sepharial's Transits and Planetary Periods
(1920, public domain) plus a small table of traditional house
significations. The day-level line also shows its rank out of the 4
defined levels, e.g. "Notable (2/4)". Docs (CLAUDE.md, README,
docs/input-output-format.md, docs/reading.md) updated to match,
including a full worked example in docs/reading.md.

interpreter/src/narrative.h

@@ -0,0 +1,46 @@
+#ifndef DECK_NARRATIVE_H
+#define DECK_NARRATIVE_H
+
+#include <stdio.h>
+
+/* Header-only dependency on the engine, same policy as significance.h -
+ * see its comment for why. */
+#include "../../engine/src/astro.h"
+
+/* Condensed, public-domain descriptions of what each transiting planet
+ * classically signifies, sourced from Sepharial's "Transits and
+ * Planetary Periods" (1920, public domain - res/Transits_and_Planetary_
+ * Periods.pdf), Chapter VIII "Effects of Transits" (pp. 60-61). The
+ * chapter's own structure - a base description of the planet's transit,
+ * plus a "well aspected"/"badly aspected" addendum - maps directly onto
+ * transiting-planet + aspect-type, our existing Aspect fields, so no new
+ * engine data is needed to use it.
+ *
+ * The Moon and Pluto aren't covered by that chapter (fast lunar transits
+ * were outside a year-ahead-forecasting book's scope; Pluto wasn't
+ * discovered until 1930, a decade after this book) - their text in
+ * narrative.c is original, written for this project in a matching
+ * voice, not drawn from Sepharial.
+ *
+ * Prints a narrative sentence for `aspect`'s transiting planet to `out`,
+ * indented with `indent` and followed by a newline - or prints nothing
+ * if the source material has no text applicable to this planet/aspect
+ * combination (e.g. an exactly neutral conjunction to a planet whose
+ * only text is a "well/badly aspected" addendum, like the Sun). A
+ * conjunction is treated as neutral - neither the "harmonious" nor the
+ * "discordant" addendum is shown for it - since Sepharial's own text
+ * says a conjunction "takes the nature of what it conjoins," something
+ * this data doesn't model.
+ *
+ * `transiting_house` is the whole-sign house (1-12) the transiting
+ * planet currently occupies in the natal chart - i.e.
+ * reading->transits.bodies[aspect->transiting_planet].house - and names
+ * *which area of life* the transit is playing out in, the standard,
+ * personalized way transits are read (see astro.h's own house-field
+ * comment). Pass a value outside 1-12 (e.g. the "no data" sentinel `0`
+ * used elsewhere - see reading_io.c's parse_bodies()) to omit that
+ * framing and print the planet's narrative on its own. */
+void narrative_print(FILE *out, const char *indent, const Aspect *aspect,
+                      int transiting_house);
+
+#endif