Extract runtime and launch targets to mk/runtime/run.mk

[pbalduino]

Parent Issue

Part of #352 - Makefile refactoring

Objective

Keep launch targets like run, console, shell, and QEMU configuration together in a dedicated runtime file.

Scope

Extract from root Makefile:

• Lines ~234: Launch target definitions
• Lines ~321: Console/shell targets
• Lines ~695: QEMU configuration and runtime setup
• Related runtime environment variables

Target Location

mk/runtime/run.mk

Implementation Steps

1. Create mk/runtime/ directory structure
2. Extract QEMU configuration variables
3. Move run/console/shell target definitions
4. Update root Makefile to include mk/runtime/run.mk
5. Test make run, make console, make shell
6. Verify QEMU launches correctly

Dependencies

• #356 (kernel build - runtime needs kernel image)

Acceptance Criteria

• [ ] All runtime targets in mk/runtime/run.mk
• [ ] make run works correctly
• [ ] make console and make shell work
• [ ] QEMU configuration is clear and accessible
• [ ] No behavioral changes