Include target and suite identity in Wave case JSON reports

## Problem

Case JSON reports created by `tools/run_tests.py` contain the host identity and test results, but omit the selected target id, target triple, executor, and selected suites. Artifacts from cross and WebAssembly matrix jobs therefore require their filename and workflow context to be interpreted.

## Scope

- Add selected target and suite identity to the versioned JSON report.
- Preserve a clear representation for explicit `--suite` runs.
- Add unit tests without invoking the full compiler.
- Document the fields in the test guide tracked by #357.

## Completion criteria

- Reports identify target id/triple, executor, and ordered suites where applicable.
- Native auto-selection and explicit suites are distinguishable.
- Existing summary and per-test records remain compatible or receive an explicit schema version.

Related: #457

Start by reading tools/run_tests.py and tracing how its versioned JSON report is assembled, including target, executor, and suite selection. Add focused unit tests without invoking the full compiler, then update the test guide tracked by #357. Done means reports distinguish native auto-selection from explicit suites, identify target and executor details, and preserve or explicitly version existing records.

Written by the indexing model from the issue text.