Make pred inspect respect exact problem variants

[isPANN]

Summary

• query outgoing reductions from the loaded problem exact variant
• report only witness-executable reductions, matching pred reduce defaults
• render non-default target variants as directly reusable slash specs
• apply the same behavior to CLI and MCP inspection

Verification

• make check
• regression tests execute every target advertised by inspect
• regression coverage separates unit and weighted sibling variants
• regression coverage excludes non-witness reductions

Stacked on #1083.

Fixes #1114

[Copilot]

Pull request overview

This PR updates pred inspect (CLI and MCP) to compute reduces_to from the loaded problem’s exact normalized variant, and to list only witness-executable reductions (matching pred reduce defaults). It also renders non-default target variants as reusable slash specs (e.g., Name/Variant/...) and adds regression coverage to ensure every advertised inspection target is actually reducible.

Changes:

• Add ReductionGraph::outgoing_reductions_from(...) to query outgoing reductions for an exact variant and reduction mode.
• Update CLI + MCP inspection to derive targets from the exact variant and filter to witness-capable reductions, formatting non-default targets as slash specs.
• Add unit + CLI regression tests covering exact-variant separation and witness-only inspection output.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/rules/graph.rs	Adds an exact-variant outgoing reduction query API used by inspection logic.
src/unit_tests/rules/graph.rs	Adds unit tests verifying exact-variant and mode filtering behavior, plus unknown-variant rejection.
problemreductions-cli/src/commands/inspect.rs	Switches inspection to exact-variant, witness-executable targets and formats non-default variants as slash specs.
problemreductions-cli/src/mcp/tools.rs	Aligns MCP inspection output with the updated CLI inspection behavior.
problemreductions-cli/tests/cli_tests.rs	Adds CLI regressions ensuring inspect advertises only executable targets and excludes non-witness reductions.

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