fix: enforce 1:1 compose path mapping for Pilot agent mounts (#1516)

* fix: enforce 1:1 compose path mapping for Pilot agent mounts

Pilot enrollment now generates validated 1:1 bind mounts so every
agent path maps to a unique compose directory. Persisted agent paths
reconcile during startup to catch drift. Unsafe relative-bind redeploys
are blocked before container removal to prevent path escapes.

- Add composePathMapping utility with strict path validation
- Generate COMPOSE_DIR and validated mounts during Pilot enrollment
- Reconcile persisted agent paths during startup bootstrap
- Block redeploy when a relative-bind mount would escape the compose root
- Default Pilot UI path to /opt/docker/sencho
- Update multi-node and pilot-agent documentation
- Add regression tests for enrollment, bootstrap, compose-service,
  and environment-check paths

* fix: update E2E enrollment regexes for YAML-quoted token values

backend/src/utils/composePathMapping.ts

@@ -0,0 +1,50 @@
+import path from 'path';
+
+export interface BindPathMapping {
+  source: string;
+  destination: string;
+}
+
+function normalizePath(value: string): string {
+  if (value === '/' || /^[A-Za-z]:[\\/]?$/.test(value)) return value;
+  return value.replace(/[\\/]+$/, '');
+}
+
+function isAtOrBelow(candidate: string, base: string): boolean {
+  const resolvedCandidate = path.resolve(candidate);
+  const resolvedBase = path.resolve(base);
+
+  // After resolution, verify the candidate still starts with the base followed
+  // by a separator (or is an exact match). This catches `..` segments that
+  // would pass a naive string-prefix check but escape the intended directory.
+  if (resolvedCandidate === resolvedBase) return true;
+  // Filesystem root: any resolved absolute path is at or below it.
+  if (resolvedBase === path.resolve('/')) return path.isAbsolute(resolvedCandidate);
+  if (/^[A-Za-z]:[\\/]?$/.test(resolvedBase)) {
+    return resolvedCandidate.toLowerCase().startsWith(resolvedBase.slice(0, 2).toLowerCase());
+  }
+  return resolvedCandidate.startsWith(resolvedBase + path.sep);
+}
+
+/** Resolve a container-visible path to the corresponding host bind path. */
+export function resolveHostBindPath(
+  containerPath: string,
+  mounts: ReadonlyArray<BindPathMapping>,
+): string | null {
+  const target = normalizePath(containerPath);
+  const match = mounts
+    .filter((mount) => isAtOrBelow(target, normalizePath(mount.destination)))
+    .sort((a, b) => normalizePath(b.destination).length - normalizePath(a.destination).length)[0];
+  if (!match) return null;
+
+  const destination = normalizePath(match.destination);
+  const source = normalizePath(match.source);
+  const suffix = target.slice(destination.length).replace(/^[\\/]+/, '');
+  if (!suffix) return source;
+  const separator = source.endsWith('/') || source.endsWith('\\') ? '' : '/';
+  return `${source}${separator}${suffix}`;
+}
+
+export function pathsMatch(left: string, right: string): boolean {
+  return normalizePath(left) === normalizePath(right);
+}