Consolidate Render cron services into a single time-gated dispatcher

Instead of creating a separate Render cron service for each scheduled task (each with its own build step, env vars, secret group attachments, and billing), consolidate into a single frequently-running cron service that dispatches based on the current time.

Pattern:

# Single cron service running every 10 minutes (*/10 * * * *)
set -o errexit

# Always-run tasks
python -m myapp do-frequent-thing

# Time-gated tasks
HOUR=$(date -u +%H)
MINUTE=$(date -u +%M)

if [ "$HOUR" = "10" ] && [ "$MINUTE" = "30" ]; then
    python -m myapp do-morning-thing
fi

if [ "$HOUR" = "21" ] && [ "$MINUTE" = "00" ]; then
    python -m myapp do-evening-thing
fi

Requirements:

• The scheduled times must align with the dispatcher's cron interval (e.g. */10 hits :00, :10, :20, :30, :40, :50 — so 10:30 and 21:00 both hit exactly)
• The dispatched tasks should be idempotent so timing jitter or double-fires are harmless
• Tasks should enqueue work to a job queue rather than running inline, keeping the cron service lightweight

Benefits:

• Fewer services = less build time, lower billing, fewer manual secret-group attachments
• Single place to see all scheduled dispatch logic
• Shared env/secrets without per-service dashboard configuration