Add haf-app-tools: shared utilities for HAF applications

This adds a new haf-app-tools directory containing scripts and utilities
that HAF applications (balance_tracker, haf_block_explorer, hafah, hivemind)
currently obtain via the haf submodule.

By centralizing these tools here, apps can fetch them at runtime instead
of including the entire haf repository as a submodule, significantly
simplifying the dependency chain.

Contents:
- scripts/common.sh: Shared bash utilities (logging, git clone helpers)
- scripts/create_haf_app_role.sh: PostgreSQL role creation for HAF apps
- scripts/copy_datadir.sh: Data directory copying with NFS cache fallback
- python/process_openapi.py: OpenAPI to SQL/nginx generator
- config/config_5M.ini: Standard hived config for 5M block testing

Also includes migration documentation in docs/haf-app-tools-migration.md.