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/README.md

@@ -0,0 +1,59 @@
+# Deck in a Dash - Pebble watch app
+
+The actual watchapp: shows the same daily tarot + astrology reading as
+`dist/run-interpreter.sh`, computed entirely on-device (no companion
+app, no server - birth data, language, and notification settings are
+entered via a Pebble config page and persisted on-watch).
+
+## Layout
+
+```
+watch/
+  package.json     Pebble app manifest (uuid, targetPlatforms, messageKeys, resources)
+  wscript           waf build rules - see its own top-of-file comment for
+                    why this app's C sources are NOT a plain src/c/**/*.c
+                    glob (most of the actual logic lives in ../engine/src/,
+                    shared byte-for-byte with the desktop deck-engine/
+                    interpreter-cli binaries)
+  src/c/            Watch-only C: UI, persisted config, on-device reading
+                    orchestration, daily notification wakeup
+  src/pkjs/         pkjs config webview (birth data/language/notification
+                    settings) - a self-contained `data:` URI form, no
+                    server
+  resources/        Bitmap resources (card art, app icon) - resources/img/
+                    is generated (gitignored), see below
+  scripts/          Build-time codegen: gen_i18n_tables.py (translation
+                    tables from ../engine/i18n/*.lang) and
+                    gen_card_images.py (downsized card art from
+                    ../res/img/*.jpeg) - both run automatically by
+                    wscript on every `pebble build` (see its own comment
+                    for why that stays cheap on repeat builds)
+```
+
+## Building
+
+Requires the Pebble SDK/tool (`pebble` CLI) and Pillow (`pip install
+Pillow`, used only by gen_card_images.py) - neither is part of this
+repo's own `make`/`make test` toolchain, which only builds the desktop
+`deck-engine`/`interpreter-cli` binaries. From this directory:
+
+```bash
+pebble build     # -> build/watch.pbw
+```
+
+The root Makefile's `make watchapp` target wraps this and copies the
+resulting `.pbw` into `dist/`, versioned the same way as `make package` -
+see the root CLAUDE.md's "Packaging" section.
+
+## Platform support
+
+`targetPlatforms` deliberately excludes **aplite** (original Pebble /
+Pebble Steel). A Pebble app's entire code+data+bss footprint shares one
+64KB region on basalt-class platforms, but only 24KB on aplite - and
+even this project's minimal skeleton (blank window + one
+`reading_generate()` call, no UI/config/persistence/notification code
+yet) already uses 19KB of it, leaving only ~5.5KB of headroom. That's
+not enough room for the multi-screen UI, on-watch config persistence,
+and wakeup-based daily notification this app still needs to add -
+basalt and newer (chalk/diorite/emery/flint/gabbro) all have comfortable
+46-112KB of free heap for the same skeleton.