[M1] Refactor package structure to MCP-aligned architecture

[rdobrik]

Description

Restructure camel-a2a-component code into modular packages aligned with CamelMcpComponent patterns:

• model
• processor
• catalog
• service
• config

Move existing classes to appropriate packages and keep backward compatibility where feasible.

Tasks

• Create package directories and migrate existing classes.
• Introduce shared constants class for exchange property keys.
• Remove ad hoc protocol logic from producer/consumer classes.
• Update imports and tests.

Acceptance Criteria

• Project compiles without package conflicts.
• Existing tests pass after migration.
• No behavior regression in currently supported flows.

Dependencies

• None