Add manual-only translation mode, mapping provenance, and actionable auto-mapping diagnostics

[Copilot]

This change introduces explicit translation-control modes and makes mapping selection provenance first-class in plan/runtime diagnostics. It enforces manual-only behavior when requested, preserves explicit relationships under fill-missing behavior, and adds targeted diagnostics for automatic, ambiguous, and unsupported mappings.

• Translation control in CompilerOptions

  • Added AutoTranslationMode with:
    • Off → manual relationships only
    • FillMissingOnly (default) → auto-select only for uncovered rules
  • Added WarnOnAutomaticMappings (default true) to emit warning diagnostics for every auto-selected mapping.

• First-class mapping provenance

  • Added MappingSelectionProvenance (Explicit, Automatic) to selected mappings.
  • Carried provenance into:
    • RuleCoverageSummary
    • MappingDecisionReport
    • runtime mapping-provenance diagnostics
  • Added RuntimeDiagnosticReport.MappingSummary with counts:
    • explicit mappings used
    • automatic mappings used
    • missing mappings
    • ambiguous mappings

• Manual-only and fill-missing enforcement

  • AutoTranslationMode.Off now fails compilation when any source rule lacks an explicit relationship.
  • Failure messages enumerate missing source rules and direct users to define manual relationships.
  • FillMissingOnly preserves explicit mappings as authoritative and auto-selects only remaining uncovered rules.

• Ambiguity/unsupported guidance and reliability integration

  • Added ambiguity diagnostics for close-confidence candidate sets, including top candidates and margin.
  • Added manual-required diagnostics for unsupported/uncovered rules.
  • Reliability violations now use explicit messages tied to:
    • unsupported mappings requiring manual relationships
    • ambiguous automatic mappings requiring manual relationships
    • automatic-mapping determinism concerns

• Tests and docs updates

  • Expanded CDTk.Tests/UnitTest1.cs for:
    • manual-only failure on missing relationships
    • fill-missing partial semantics with per-auto warnings
    • explicit mapping non-override
    • ambiguity diagnostics
    • manual-required unsupported diagnostics
  • Updated README.md, docs/troubleshooting.md, and docs/release-readiness.md to document new options, diagnostics, and migration path.

var options = new CompilerOptions
{
    ReliabilityPolicy = TranslationReliabilityPolicy.Permissive,
    AutoTranslationMode = AutoTranslationMode.Off,   // require explicit relationships
    WarnOnAutomaticMappings = true
};

var compiler = new Compiler(sourceGrammar, targetGrammar, semantics, options);
var report = compiler.CompileSource(input).ToDiagnosticReport();
// report.MappingSummary + report.Decisions now expose explicit vs automatic provenance