Introduces watch/, a real Pebble watchapp (built via pebble build) that

shows the daily tarot/astrology reading on-device: persistence, reading
computation, and UI screens, driven by the existing engine/interpreter
code linked in unchanged where possible.

Required engine-side changes to make that linking work:
- A compact low-precision ephemeris (lowprec_ephemeris.c) replacing the
  vendored ~127KB Astronomy Engine, which doesn't fit the watch's ~64KB
  app budget.
- Hand-rolled sqrt/atan2/sin/cos replacements for that ephemeris and
  astro.c's Ascendant calculation - Pebble's statically-linked libm
  hard-faults on real hardware under this app's -fPIE link for all four.
- narrative.c/guidance.c refactored from FILE*/fprintf onto snprintf-
  based buffers, since Pebble's SDK blocks fprintf at compile time.

interpreter/src/narrative.h

@@ -1,12 +1,20 @@
 #ifndef DECK_NARRATIVE_H
 #define DECK_NARRATIVE_H
 
-#include <stdio.h>
+#include <stddef.h>
 
 /* Header-only dependency on the engine, same policy as significance.h -
  * see its comment for why. */
 #include "../../engine/src/astro.h"
 
+/* Generous upper bound on narrative_write()'s output (indent + house
+ * framing + base + harmonious/discordant addendum + newline) across
+ * every language this project ships a translation for - callers on
+ * constrained platforms (the watch) are free to size their own stack
+ * buffer smaller if they know their own strings are shorter; this is
+ * just a safe default for a caller that doesn't want to think about it. */
+#define NARRATIVE_TEXT_MAX 512
+
 /* 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_
@@ -22,15 +30,19 @@
  * 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
+ * Writes a narrative sentence for `aspect`'s transiting planet into
+ * `buf` (a caller-supplied buffer of `buf_size` bytes, always left
+ * null-terminated - NARRATIVE_TEXT_MAX is a safe size), indented with
+ * `indent` and followed by a newline - or writes an empty string 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.
+ * this data doesn't model. Uses only snprintf() internally (never
+ * fprintf/sprintf/vsnprintf, all of which Pebble's SDK blocks at compile
+ * time), so this function links into the watch app unchanged.
  *
  * `transiting_house` is the whole-sign house (1-12) the transiting
  * planet currently occupies in the natal chart - i.e.
@@ -44,9 +56,9 @@
  * Every string here is looked up via i18n_get() under "narrative.*"
  * keys (engine/i18n's .lang files) before falling back to the English text
  * baked into narrative.c, the same catalog tarot_data.c uses - so this
- * text respects whatever --lang the caller loaded with i18n_load()
- * (main.c does so before calling this). */
-void narrative_print(FILE *out, const char *indent, const Aspect *aspect,
+ * text respects whatever --lang the caller loaded with i18n_load()/
+ * i18n_load_table() (main.c does so before calling this). */
+void narrative_write(char *buf, size_t buf_size, const char *indent, const Aspect *aspect,
                       int transiting_house);
 
 #endif