[Feature]: As a process developer, I want to be warned when a call activity does not pass the variables its target process reads

[emaarco]

Summary

As a process developer, I want to be warned when a call activity omits input variables that the called process reads, so that the subprocess does not start with missing inputs.

Motivation

Missing input mappings surface only at runtime as null/undefined variables in the called process.

Proposed Solution

• New opt-in CrossModelValidationRule (call-activity-input-coverage, WARN).
• Per call activity: resolve the target via resolveCalledModel(...), compare its read variables (VariableDirection.INPUT) against the caller's inputMappings.target; propagateAllInputVariables == true covers everything.
• No domain change — reuses existing variables + inputMappings.
• Document the heuristic: "required" is not modeled in BPMN, hence WARN, not ERROR.

Acceptance Criteria

• Warns when the target reads an input variable the caller neither maps nor propagates
• No warning when propagateAllInputVariables = true
• Opt-in (not in BpmnRules.all()), core unit test + integration test, docs