Automate direct finite-symbol stability tactic

[PerAlexandersson]

Summary

• add rr_finite_symbol_stable_or_zero_auto for goal-directed operator/input inference and local certificate discovery
• delegate through the existing inferred frontend so all forms invoke the proved finiteSymbol_preserves_stability declaration at one site
• test selection in the presence of decoy operator and input stability certificates

API boundary

This is only the direct multiaffine stable-or-zero theorem surface. It does not discharge the false legacy homogeneous finite-symbol statement, the conjectural Jensen-pencil implication, the degree-d PF-bidiagonal backend, or an affine-bidiagonal application bridge.

Verification

• focused external-cache build: RealRooted.Tactic.Examples.FiniteSymbol
• full external-cache build: RealRooted (8,951 jobs; only pre-existing warnings)
• python3 scripts/check_root_imports.py
• git diff --check and touched-file line/placeholder scans
• Claude Opus/max API and macro review; deduplication and decoy-certificate recommendation applied