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.

engine/src/i18n.h

@@ -9,11 +9,27 @@
  * file can't be opened (the catalog is left as it was in that case).
  *
  * This uses stdio, so - like main.c and reading_print_text/_html - it's
- * a desktop-only entry point, not something the Pebble watchapp will
- * call as-is. i18n_get() below is a pure table lookup, so it's fine to
- * port; the watchapp will just need its own (non-file-based) way to
- * populate the catalog, e.g. from a compiled-in resource. */
+ * a desktop-only entry point: Pebble's SDK doesn't provide fopen/fgets
+ * at all (a compile-time error, not just a runtime failure), so this
+ * function isn't even compiled when building for the watch (guarded
+ * #ifndef PBL_SDK_3 in i18n.c) - see i18n_load_table() below, its
+ * watch-side equivalent. */
+#ifndef PBL_SDK_3
 bool i18n_load(const char *path);
+#endif
+
+/* The watch's non-file-based equivalent of i18n_load(): points i18n_get()
+ * at two parallel arrays (keys[i] -> values[i], `count` entries) instead
+ * of parsing a file - for a compiled-in translation table generated from
+ * engine/i18n's .lang files at watch-app build time (see the watch
+ * app's own build tooling). Zero-copy - just stores the three pointers -
+ * so `keys`/`values` must outlive the call (a `static const char *const`
+ * array is the expected caller, living in flash/ROM, not a local/heap
+ * buffer). This is what keeps the watch from needing i18n_load()'s
+ * ~140KB g_entries[] catalog, which its RAM budget can't afford.
+ * Available on every platform, since it has no platform-specific
+ * dependencies, but only the watch actually calls it today. */
+void i18n_load_table(const char *const *keys, const char *const *values, int count);
 
 /* Returns the translation for `key` from the loaded catalog, or
  * `fallback` if no catalog is loaded or `key` isn't in it. Every caller