Add Region & Scope system foundation (MeshCore 1.10.0+)

Phase 1: Core Infrastructure and Design

EEPROM Structure Changes (v5):
- Extended NodeConfig with regions array (8 regions × 8 chars)
- Added regionCount field for tracking configured regions
- Default configuration includes wildcard "*" for backward compatibility
- EEPROM_VERSION bumped from 4 to 5
- Memory impact: +65 bytes to NodeConfig (~175 bytes total)

Files Modified:
- src/main.h: Added MC_MAX_REGIONS (8), MC_REGION_LEN (8) defines
- src/core/Config.h: Updated NodeConfig struct and EEPROM_VERSION
- src/core/Config.cpp: Updated defaultConfig with wildcard "*"

Design Document:
- docs/REGION_SCOPE_DESIGN.md: Complete implementation plan
  - Architecture overview with components and data flow
  - 9-phase implementation roadmap
  - MeshCore protocol analysis (transport codes)
  - RegionManager class design
  - CLI commands specification
  - Packet filtering logic design
  - Testing strategy and examples
  - Backward compatibility guarantees
  - Performance and memory impact analysis

Key Features (Planned):
- Geographic packet filtering via scope matching
- Hierarchical region matching (e.g., "us" matches "us-co")
- Wildcard "*" for global forwarding (backward compat)
- Up to 8 configurable regions per repeater
- CLI commands: get/set/add/remove region
- MeshCore 1.10.0+ transport code support

Backward Compatibility:
- Default wildcard "*" forwards all packets
- Legacy FLOOD/DIRECT packets (no scope) always forwarded
- No breaking changes for existing deployments
- Gradual adoption path documented

Next Steps (Phase 2-9):
- Implement RegionManager class (src/mesh/RegionManager.h)
- Add transport code parsing to Packet.h
- Integrate scope filtering in shouldForward()
- Add CLI commands for region management
- Create test suite (tools/test_region_scope.py)
- Update documentation (API.md, COMMANDS.md)

This commit establishes the foundation for full Region & Scope
support. The system is designed but not yet functional - development
continues in subsequent phases as documented in REGION_SCOPE_DESIGN.md.

Author: atomozero