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/web/server.ts

@@ -40,7 +40,7 @@ import { existsSync, mkdirSync, readFileSync, chmodSync, rmSync, statSync } from
 import fs from 'node:fs/promises';
 import { execSync } from 'node:child_process';
 import { hostname as getHostname } from 'node:os';
-import { dataPath } from '../config/instance.js';
+import { dataPath, getDataDir, CODEMAN_INSTANCE } from '../config/instance.js';
 import { getHookSecret } from '../config/hook-secret.js';
 import { EventEmitter } from 'node:events';
 import { Session, isExternalCliMode, type BackgroundTask } from '../session.js';
@@ -1941,6 +1941,20 @@ export class WebServer extends EventEmitter {
     // CRITICAL: Skip in test mode to prevent tests from picking up user sessions
     if (!this.testMode) {
       await this.restoreMuxSessions();
+
+      // Instance-scoped reaper: after restore, `docker rm -f` managed containers of
+      // THIS instance whose case is gone from docker-cases.json (best-effort, never
+      // touches another instance's containers). Runs after restore so containers
+      // still referenced by a restored session are preserved.
+      void import('../docker-hosts.js')
+        .then(({ reapOrphanedDockerContainers }) => reapOrphanedDockerContainers(getDataDir(), CODEMAN_INSTANCE))
+        .then((reaped) => {
+          if (reaped.length > 0)
+            console.log(`[Docker] reaped ${reaped.length} orphaned container(s): ${reaped.join(', ')}`);
+        })
+        .catch(() => {
+          /* best-effort — daemon may be absent */
+        });
     }
 
     // Clean up stale sessions from state file that don't have active mux sessions