refactor: modularize CI workflows with centralized variables

Split monolithic ci.yaml (448 lines) into 6 specialized workflows.
Refactored ci.yaml as orchestrator (118 lines) with centralized variable
calculation. All workflows support workflow_call, workflow_dispatch, and
standalone execution. Eliminates duplicate variable calculations.

Signed-off-by: Carlos Eduardo Arango Gutierrez <[email protected]>

Author: ArangoGutierrez