feat(docker): export/import (move a container to another machine) + boot reaper

- src/docker-export.ts: full-image export (pause-consistent commit + save|stream +
  workspace tar + manifest -> one .codeman-container.tgz) and workspace-only; import
  validates manifest + per-member sha256, traversal-guards the workspace tar, docker
  load + quarantine re-tag (never overwrites a local tag). Bounded by
  runWithConversionLimit; free-space precheck; docker rmi in finally; sealed
  containers refuse full-image export.
- routes: POST /api/docker-cases/:name/export (background + SSE), GET/DELETE
  /api/docker-exports, GET download, POST /api/docker-cases/import (-> new host+case)
- instance-scoped boot reaper (docker-hosts.reapOrphanedDockerContainers) wired after
  restoreMuxSessions; never touches another instance's containers
- SSE docker:exportComplete/exportFailed/importComplete (both registries)
- fix: stream pipeline in saveImageToTar so the bundle isn't truncated

VERIFIED end-to-end on real docker: full export -> 326MB valid bundle -> delete
case -> import -> new container runs from the quarantined image with the workspace
file AND the in-image change both restored.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/docker-hosts.ts

@@ -545,6 +545,59 @@ export async function checkDockerTmuxAvailable(
   }
 }
 
+/**
+ * Instance-scoped boot reaper: `docker rm -f` any MANAGED container that belongs
+ * to THIS instance (by the `codeman.instance` label) but whose case is no longer
+ * in `docker-cases.json`. The instance scoping is what stops a beta from reaping
+ * prod's containers (the cross-instance hazard). No-op under VITEST. Best-effort.
+ */
+export async function reapOrphanedDockerContainers(
+  configDir: string,
+  instance: string,
+  engine: DockerEngine = 'docker'
+): Promise<string[]> {
+  if (IS_TEST_MODE) return [];
+  const bin = engine === 'podman' ? 'podman' : 'docker';
+  let rows: Array<{ name: string; inst: string }> = [];
+  try {
+    const { stdout } = await execFileAsync(
+      bin,
+      [
+        'ps',
+        '-a',
+        '--filter',
+        'label=codeman.managed=1',
+        '--format',
+        '{{.Names}}\t{{index .Labels "codeman.instance"}}',
+      ],
+      { timeout: DOCKER_PROBE_TIMEOUT_MS }
+    );
+    rows = stdout
+      .split('\n')
+      .filter(Boolean)
+      .map((line) => {
+        const [name, inst = ''] = line.split('\t');
+        return { name, inst };
+      });
+  } catch {
+    return []; // daemon down / engine absent — nothing to reap
+  }
+  const cases = await readDockerCases(configDir);
+  const expected = new Set(cases.map((c) => c.container ?? dockerContainerName(c.name)));
+  const reaped: string[] = [];
+  for (const { name, inst } of rows) {
+    if (inst !== instance) continue; // only THIS instance's containers
+    if (expected.has(name)) continue; // still referenced by a live case
+    try {
+      await execFileAsync(bin, ['rm', '-f', name], { timeout: DOCKER_PROBE_TIMEOUT_MS });
+      reaped.push(name);
+    } catch {
+      /* best-effort */
+    }
+  }
+  return reaped;
+}
+
 /**
  * Read the IN-CONTAINER Claude CLI version (`docker exec <container> claude
  * --version`). Feeds Session.cliVersion for docker sessions (the LOCAL claude