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/build

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+# Build or rebuild the derp container image.
+# Usage: tools/build [--no-cache]
+
+# shellcheck source=tools/_common.sh
+source "$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/_common.sh"
+cd "$PROJECT_DIR" || exit 1
+
+args=()
+[[ "${1:-}" == "--no-cache" ]] && args+=(--no-cache)
+
+dim "Building image..."
+$COMPOSE build "${args[@]}"
+
+size=$(podman image inspect "$IMAGE_NAME" --format '{{.Size}}' 2>/dev/null || true)
+if [[ -n "$size" ]]; then
+    human=$(numfmt --to=iec-i --suffix=B "$size" 2>/dev/null || echo "${size} bytes")
+    info "Image built ($human)"
+else
+    info "Image built"
+fi