feat: container management tools in tools/

Shell scripts for build, start, stop, restart, nuke, logs, status.
Shared helpers in _common.sh (colours, compose detection, project root).
Updated CHEATSHEET.md with new tool references.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tools/nuke

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+# Full teardown: stop container and remove image.
+# Usage: tools/nuke
+
+# shellcheck source=tools/_common.sh
+source "$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/_common.sh"
+cd "$PROJECT_DIR" || exit 1
+
+dim "Stopping container..."
+$COMPOSE down 2>/dev/null || true
+
+before=$(podman system df --format '{{.Size}}' 2>/dev/null | head -1 || true)
+
+dim "Removing image..."
+podman rmi "$IMAGE_NAME" 2>/dev/null || true
+# Also remove any dangling derp images
+podman images --filter "reference=*derp*" --format '{{.ID}}' 2>/dev/null | \
+    xargs -r podman rmi 2>/dev/null || true
+
+after=$(podman system df --format '{{.Size}}' 2>/dev/null | head -1 || true)
+
+if [[ -n "$before" && -n "$after" ]]; then
+    info "Teardown complete (images: $before -> $after)"
+else
+    info "Teardown complete"
+fi