costco-watch: ntfy alert when a Costco tire is back in stock

apps/costco-watch/build/README.md

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+# costco-watch image
+
+Dependency-free Node service (node:22-alpine + curl for the healthcheck).
+Source: https://git.alexzaw.dev/alexz/costco-watch (working copy:
+~/projects/costco-watch). Build + push with ./build.sh.
+
+Gotchas:
+- TARGET_URL must go through the costco-tire cloudflared proxy AND that
+  hostname needs a Cloudflare Transform Rule adding browser headers
+  (User-Agent, Accept, Accept-Language, Sec-Fetch-*). Without it Costco stalls
+  the request until timeout and the checker reports "error"/"blocked".
+- State (last stock value, transition history) lives in ${APP_DATA_DIR}/data;
+  wiping it means the next check can re-alert.

apps/costco-watch/build/build.sh

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+#!/bin/bash
+set -euo pipefail
+IMAGE_NAME="${IMAGE_NAME:-git.alexzaw.dev/alexz/costco-watch}"
+IMAGE_TAG="${IMAGE_TAG:-latest}"
+SRC="${SRC:-$HOME/projects/costco-watch}"
+docker build "$@" -t "${IMAGE_NAME}:${IMAGE_TAG}" "$SRC"
+docker push "${IMAGE_NAME}:${IMAGE_TAG}"