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/start

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+# Start the derp container.
+# Usage: tools/start
+
+# shellcheck source=tools/_common.sh
+source "$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/_common.sh"
+cd "$PROJECT_DIR" || exit 1
+
+# Build first if no image exists
+if ! podman image exists "$IMAGE_NAME" 2>/dev/null; then
+    dim "No image found, building..."
+    "$SCRIPT_DIR/build"
+    echo
+fi
+
+dim "Starting container..."
+$COMPOSE up -d
+
+sleep 3
+dim "Recent logs:"
+podman logs --tail 15 "$CONTAINER_NAME" 2>&1 || true
+echo
+info "Container started"