feat(merger): path-relative resolution — ork run/validate works from any directory

[iAlexeze]

Summary

• pkg/merger/file.go: crdFile, crFiles, setup.apply, and Komposer imports.files are now resolved relative to the declaring file, not the working directory
• cmd/cli/files.go: CLI-provided -f paths are converted to absolute on intake so downstream resolution is always anchored correctly
• examples/use-cases/full-stack-app: all six sub-katalogs switched from apiTypes: to crdFile: — manual kubectl apply -f crd.yaml pre-step eliminated from every walkthrough
• 03-cross-crd/crd.yaml split into crd-managed-database.yaml + crd-database-backed-app.yaml; 06-full-stack uses setup: block to pull in the managed-database dependency
• Minor docs fixes: getting-started CLI table, e2e schema headings

Test plan

• ork run -f /absolute/path/katalog.yaml works from any directory
• ork run (no -f) still resolves CRDs from the current directory
• ork e2e on 03-cross-crd passes with split CRD files
• ork e2e on 06-full-stack applies managed-database via setup block without a manual pre-step