refactor: split docker-manager.ts into focused modules (#2501)

* refactor: split docker-manager.ts into focused modules

Extract host-env utilities, compose generation, container
lifecycle, and cleanup into separate modules. A facade
docker-manager.ts re-exports everything for backwards
compatibility.

Closes #2473

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix: remove unused imports and restrict docker-manager facade exports

- Remove unused API_PROXY_HEALTH_PORT import from container-lifecycle.ts
- Remove unused __AWF_SECCOMP_PROFILE__ declaration from compose-generator.ts
- Replace export * with explicit named re-exports in docker-manager.ts facade
  to avoid unintentionally widening the public API surface with internal-only
  constants (SQUID_PORT, *_CONTAINER_NAME, MAX_ENV_VALUE_SIZE, etc.)

Agent-Logs-Url: https://github.com/github/gh-aw-firewall/sessions/b873ac30-3e8d-449e-a571-d9e45f65dc2c

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: 3 people