Implement the differential harness and generic F# conformance manifest

Parent: #8
Blocked by: #25

Outcome

Implement the versioned differential harness described by #5 and a compiler-owned conformance manifest organized by F# language construct and observable compiler behavior.

Acceptance criteria

• A manifest describes ordered sources, signatures, target references, normalized options, expected diagnostics, artifacts, runtime probes, and comparator classes.
• Compatibility Oracle and FSharp2 lanes run in isolated roots and differ only in compiler selection.
• Focused positive and negative programs cover each declared feature row across parsing, typing, lowering, emission, loading, and execution where applicable.
• The manifest tracks language-version and option coverage and distinguishes unsupported, failed, passed, and infrastructure-error outcomes.
• Evidence proves no production fallback and supports exact, normalized, canonical-semantic, and behavioral comparisons without requiring byte-identical outputs.
• Third-party projects are integration corpora, not sources of production branches or primary feature names.
• Governed scheduling and performance statistics remain owned by #24.

Decision inputs

Issues #2, #4, #5, #6, #16, #17, and #18; ADRs 0005, 0006, 0008, 0010, 0014, 0023, and 0027.

This issue inherits the corpus-neutral acceptance policy in #8.