feat: preserve cross-scan finding relationships (#574)

* feat: preserve finding relationships in scan history

* refactor: reuse indexed finding relationships

* fix: preserve confirmed finding relationships during matching

* fix: preserve related findings throughout comparison workflows

* fix: preserve finding identities across plugin protocol versions

* fix: preserve transitive confirmed finding identities

* fix: preserve comparison identities and discover protocol support

* fix: canonicalize confirmed identities and wrapped capabilities

* test: align history fixtures with confirmed identities

* fix: include stable finding identities in linked history

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Co-authored-by: mldangelo-oai <269034524+mldangelo-oai@users.noreply.github.com>