Add root dir to determine paths for sast changed files

[attiasas]

fix(audit/sast): use root dir for SAST changed-file paths

Summary

SAST “changed files” resolution now keys off the audit root directory (the CLI root when set) instead of only the scan targets’ common parent. AuditParams carries that root, and SastChangedFilesForTarget takes a rootDir and builds absolute paths under it. Path handling is simplified by dropping extra normalization of git paths before joining to the root.

Changes

• commands/audit/auditparams.go: Add rootDir on AuditParams with SetRootDir / RootDir.
• commands/audit/audit.go: Call SetRootDir(auditCmd.rootDir) when building audit params; introduce getRootDir to use an explicit root when non-empty, otherwise scanResults.GetCommonParentPath(); pass that into SastChangedFilesForTarget.
• jas/sast/sastscanner.go: Rename the last parameter conceptually from common parent to rootDir; compute target-relative paths vs rootDir; simplify collectSastChangedAbsPaths (join commonAbs + changed path directly; remove normalizeRepoRelativeChangedPath).
• jas/sast/sastscanner_test.go: Update TestSastChangedFilesForTarget for rootDir and adjust the absolute-path case to a repo-relative changed file.

[github-actions]

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