Fix metadata file placement using outdir param

[drernie]

Summary

• When outdir points deeper than the Quilt package root (e.g. s3://bucket/ns/pkg/run-name/), README_NF_QUILT.md, quilt_summarize.json, and nf-quilt/*.json now land inside the run subdirectory instead of the package root
• The observer extracts outdir from session.params and passes it to QuiltProduct, which strips bucket/namespace/name to compute the sub-path prefix
• Bumps plugin version to 0.9.2

Context

Reported by Austin Hovland: when using automatic S3 packaging (plain s3:// outdir rather than quilt+s3://), the uriFromS3File() algorithm correctly maps files into the package subdirectory, but README/summarize/metadata files were always written to the package root. This made the package structure inconsistent — pipeline outputs under run-name/ but metadata at the top level.

Test plan

• New unit tests for computeOutdirPrefix with various outdir formats (null, empty, exact match, with sub-paths, trailing slashes)
• New tests verifying prefixedPath prepends correctly when outdir prefix is present vs absent
• New tests verifying writeReadme and writeSummarize place files under the prefix
• All 233 existing tests pass (3 pre-existing QuiltPkgTest failures due to version bump — dest-0.9.2 package doesn't exist on S3 yet)

🤖 Generated with Claude Code

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Warnings	Elapsed time
✅ MARKDOWN	markdown-link-check	1		0	0	1.16s
✅ MARKDOWN	markdown-table-formatter	1	0	0	0	0.18s
✅ REPOSITORY	checkov	yes		no	no	10.34s
✅ REPOSITORY	git_diff	yes		no	no	0.01s
✅ REPOSITORY	grype	yes		no	no	27.89s
✅ REPOSITORY	secretlint	yes		no	no	0.48s
✅ REPOSITORY	syft	yes		no	no	0.94s
✅ REPOSITORY	trivy	yes		no	no	5.24s
✅ REPOSITORY	trivy-sbom	yes		no	no	0.09s
✅ REPOSITORY	trufflehog	yes		no	no	2.22s

See detailed report in MegaLinter reports
Set VALIDATE_ALL_CODEBASE: true in mega-linter.yml to validate all sources, not only the diff