[Enhancement]: Update parser to extract path artifacts

[tomvothecoder]

Is your feature request related to a problem?

The parser does not currently extract several path-related artifacts that are needed from case configuration and runtime files.

Artifacts to collect:

• Output path: CaseDocs/env_run.xml -> RUNDIR
• Archive path: CaseDoc/senv_run.xml -> DOUT_S_ROOT
• Run script path: CaseDocs/env_case.xml -> f"{CASEROOT}/.case.run"
• Postprocessing script paths: CaseDocs/env_run.xml -> POSTRUN_SCRIPT

Describe the solution you'd like

Update the parser to extract these additional path artifacts and expose them consistently with the existing parsed outputs.

Implementation note:

• Identify the source files that store each of these values and extend the parser accordingly.

Describe alternatives you've considered

No alternative approach has been considered yet.

Additional context

Out of scope for this issue:

• Batch log path: parse from $CASEROOT/.case.run

[tomvothecoder]

Implementation plan:

1. Extend the CaseDocs XML parsers in backend/app/features/ingestion/parsers/case_docs.py to extract the path-bearing values we need from the existing source files:

   • output artifact: env_run.xml -> RUNDIR
   • archive artifact: env_run.xml -> DOUT_S_ROOT
   • run script artifact: env_case.xml -> CASEROOT, then derive ${CASEROOT}/.case.run
   • postprocessing artifact: env_run.xml -> POSTRUN_SCRIPT

2. Thread those parsed values through the existing parser pipeline in backend/app/features/ingestion/parsers/types.py, backend/app/features/ingestion/parsers/parser.py, and backend/app/features/ingestion/ingest.py so ingest can populate the already-supported artifact kinds instead of adding new schema/model types.

3. Validate every candidate path before creating an artifact:

   • normalize blank strings to null
   • resolve derived paths from CASEROOT when needed
   • check whether the path exists on the ingest host
   • if a path is missing, unresolved, or does not exist, log a warning and set the candidate to null so no broken artifact record is persisted

4. Important correction to the issue description: DOUT_S_ROOT is stored in env_run.xml in the sample archives under backend/qa/performance_archive, not env_case.xml.

5. Add focused test coverage:

   • parser unit tests for the new XML keys and blank POSTRUN_SCRIPT cases
   • parser/integration coverage proving the new values are discovered from CaseDocs
   • ingest/API tests proving valid paths become artifacts and invalid paths warn and resolve to null

6. No migration should be needed unless tests uncover a serialization gap. The backend already has artifact enum/model support for output, archive, run_script, and postprocessing_script.