Add Firmament V2 Phase 1 validation report and aetheris validate CLI

[yuechen-li-dev]

Motivation

• Make the existing Firmament V2 bound model (lets, let-record fields, arithmetic-nominals, tolerances, Forge concept applications, and record-shaped PMI) visible and auditable without adding new authoring syntax or AP242 lowering.
• Provide a deterministic, LLM-/human-friendly validation/report model so export-deferred PMI and tolerance-drop warnings are explicit and not silently ignored.
• Expose the report through the existing CLI surface so fixtures and tooling can consume firmamentV2Validation JSON.

Description

• Add a new report model and builder in Aetheris.Kernel.Firmament/FirmamentV2/FirmamentV2ValidationReport.cs that produces FirmamentV2ValidationReport with source, status, lets, concepts, pmi, exportSupport, diagnostics, and summary, and includes the Phase‑1 export matrix and deterministic status semantics (invalid, valid-with-deferred-export, valid).
• Preserve parser visibility for partially bound documents: introduce IsFatalDiagnosticCode (public) and change parse result wiring so the parse can preserve a Document while marking parse success/fatality; the report builder classifies diagnostics into fatal/warning and includes tolerance-drop warnings.
• Add a validate command to the CLI in Aetheris.CLI/CliRunner.cs exposing dotnet run --project Aetheris.CLI -- validate <file.firmament|file.firmfixture> [--json] which emits JSON rooted at firmamentV2Validation when --json is used.
• Add fixtures exercising valid-with-deferred-export, exportable-only, missing PMI tolerance, Forge missing-field, and unknown-datum cases under fixtures/FirmamentV2/Language/*, add unit tests Aetheris.Kernel.Firmament.Tests/FirmamentV2ValidationReportTests.cs, and add documentation docs/implementation/v2-phase1-r1-validation-report.md and scope-contract updates.

Testing

• Ran dotnet restore and dotnet build Aetheris.slnx -f net10.0 --no-restore /m:1, which completed successfully (build warnings only).
• Ran unit tests via dotnet test Aetheris.Kernel.Firmament.Tests/Aetheris.Kernel.Firmament.Tests.csproj with filters for validation/report/PMI-related tests; tests passed (targeted suite and new ValidationReport tests succeeded).
• Ran the new CLI validation invocation dotnet run --project Aetheris.CLI -- validate fixtures/FirmamentV2/Language/valid/v2-phase1-validation-report.valid.firmfixture --json and verified output contains firmamentV2Validation JSON with expected status (valid-with-deferred-export) and counts.
• Performed git diff --check and repository build/test validations described above as part of the change verification.

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Codex Task