feat(wallet-monitor): Slack alerts for low operator wallet balances

A one-shot monitor for the vector-marketplace box: checks each wallet in
wallets.json against a threshold (default 10 APEX) via Ogmios
(ReadOnlyOgmiosProvider) and posts a combined Slack message when any wallet is
below it. Re-reminds every 6h while a wallet stays low and posts a recovery
message when it climbs back above, deduped through a persisted state file.

Runs hourly under host cron via `docker compose run --rm` — no long-running
server, no ports/healthcheck. Reuses the buyer/supplier tsx Docker pattern and
the existing balance-query client; addresses come from a static, gitignored
wallets.json so the monitor never reads a private key.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

wallet-monitor/tsconfig.json

@@ -0,0 +1,8 @@
+{
+  "extends": "../tsconfig.base.json",
+  "compilerOptions": {
+    "rootDir": "./src",
+    "outDir": "./dist"
+  },
+  "include": ["src/**/*.ts"]
+}