feat(template): replace static /health with dependency-checking handler

Replaces the inline app.get('/health', ...) in both Workers and Node
templates with a mounted routes/health.ts handler. The new handler:

- Pings the database via pingDatabase() with a configurable timeout
  (HEALTH_DB_TIMEOUT_MS, default 2000 ms)
- Reports overall status as 'healthy' / 'unhealthy' and returns 503
  when any dependency is disconnected
- Includes version (from APP_VERSION env), uptime (seconds since module
  load — isolate uptime on Workers, process uptime on Node), timestamp,
  requestId, and a checks.database field
- Never throws to the caller: any internal error is caught and reported
  as 'disconnected' + 503, so load balancers never see a 5xx that wasn't
  caused by an actual dependency outage

Workers Bindings now declare APP_VERSION and HEALTH_DB_TIMEOUT_MS so the
template type-checks against wrangler.toml [vars] entries (added next).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Paul Mulligan