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.

watch/scripts/gen_card_images.py

@@ -0,0 +1,91 @@
+#!/usr/bin/env python3
+"""Downsizes res/img/*.jpeg into watch/resources/img/*.png for Pebble.
+
+The 22 Major Arcana JPEGs in res/img/ are ~1MB/~1086x1810px each -
+suitable for the desktop HTML reading (an <img> tag pointed at the file
+as-is) but far too large for a Pebble app's own resource budget (256KB
+total on basalt-class platforms, shared with every other resource this
+app ships). This script resizes each to CARD_WIDTH px wide (preserving
+aspect ratio) and writes a PNG per card, named after tarot_data.c's own
+k_card_slug table so watch/package.json's "resources.media" entries
+(IMG_CARD_<SLUG UPPERCASE>, file img/<slug>.png) line up without a
+separate mapping table anywhere.
+
+CARD_WIDTH=72 (-> 72x120) was picked empirically: a real `pebble build`
+of two sample cards at this size measured ~5KB/card on color platforms
+(basalt/chalk/emery/gabbro) and ~2.9KB/card on the black-and-white
+diorite/flint - so all 22 cards together cost roughly 111KB/64KB
+respectively, comfortably inside the 256KB resource budget with room
+left for other future resources (fonts, icons), while still rendering
+at close to a full basalt-class screen's height (120px of 168px).
+
+Generated output, like i18n_tables.auto.c - not committed (see
+.gitignore), regenerate by running this script directly or via the root
+Makefile's `make watchapp` (task/target that also runs `pebble build`).
+Requires Pillow (`pip install Pillow`), not part of this repo's own
+desktop build/test toolchain.
+"""
+import os
+import sys
+
+from PIL import Image
+
+SCRIPT_DIR = os.path.dirname(os.path.abspath(__file__))
+SRC_DIR = os.path.normpath(os.path.join(SCRIPT_DIR, "..", "..", "res", "img"))
+OUT_DIR = os.path.normpath(os.path.join(SCRIPT_DIR, "..", "resources", "img"))
+
+CARD_WIDTH = 72
+
+# (source file in res/img/, slug matching engine/src/tarot_data.c's
+# k_card_slug table) - in TarotCard enum order (CARD_FOOL = 0 ... CARD_WORLD).
+CARDS = [
+    ("RWS_Tarot_00_Fool.jpeg", "fool"),
+    ("RWS_Tarot_01_Magician.jpeg", "magician"),
+    ("RWS_Tarot_02_High_Priestess.jpeg", "high_priestess"),
+    ("RWS_Tarot_03_Empress.jpeg", "empress"),
+    ("RWS_Tarot_04_Emperor.jpeg", "emperor"),
+    ("RWS_Tarot_05_Hierophant.jpeg", "hierophant"),
+    ("RWS_Tarot_06_Lovers.jpeg", "lovers"),
+    ("RWS_Tarot_07_Chariot.jpeg", "chariot"),
+    ("RWS_Tarot_08_Strength.jpeg", "strength"),
+    ("RWS_Tarot_09_Hermit.jpeg", "hermit"),
+    ("RWS_Tarot_10_Wheel_of_Fortune.jpeg", "wheel_of_fortune"),
+    ("RWS_Tarot_11_Justice.jpeg", "justice"),
+    ("RWS_Tarot_12_Hanged_Man.jpeg", "hanged_man"),
+    ("RWS_Tarot_13_Death.jpeg", "death"),
+    ("RWS_Tarot_14_Temperance.jpeg", "temperance"),
+    ("RWS_Tarot_15_Devil.jpeg", "devil"),
+    ("RWS_Tarot_16_Tower.jpeg", "tower"),
+    ("RWS_Tarot_17_Star.jpeg", "star"),
+    ("RWS_Tarot_18_Moon.jpeg", "moon"),
+    ("RWS_Tarot_19_Sun.jpeg", "sun"),
+    ("RWS_Tarot_20_Judgement.jpeg", "judgement"),
+    ("RWS_Tarot_21_World.jpeg", "world"),
+]
+
+
+def main():
+    os.makedirs(OUT_DIR, exist_ok=True)
+    written = 0
+    for src_name, slug in CARDS:
+        src_path = os.path.join(SRC_DIR, src_name)
+        out_path = os.path.join(OUT_DIR, f"{slug}.png")
+
+        # wscript runs this on every `pebble build` (like gen_i18n_tables.py)
+        # so a full 22-image resize must be cheap on the common no-op case -
+        # skip any card whose output is already newer than its source JPEG.
+        if os.path.exists(out_path) and os.path.getmtime(out_path) >= os.path.getmtime(src_path):
+            continue
+
+        with Image.open(src_path) as img:
+            ratio = CARD_WIDTH / img.width
+            height = round(img.height * ratio)
+            resized = img.convert("RGB").resize((CARD_WIDTH, height), Image.LANCZOS)
+            resized.save(out_path, "PNG", optimize=True)
+        written += 1
+
+    print(f"wrote {written}/{len(CARDS)} card images to {OUT_DIR}", file=sys.stderr)
+
+
+if __name__ == "__main__":
+    main()