feat: add deterministic model glob selection

[AviBackToBlack]

Summary

Implement the first production slice of the v0.3 model-selection contract from #19 without enabling compatibility overrides yet.

This PR:

• adds optional top-level model_globs configuration while keeping existing exact models semantics unchanged
• allows glob-only configs without requiring a dummy models = []
• expands globs with case-sensitive fnmatchcase semantics
• preserves exact selectors first, then glob declaration order, with lexical ordering inside each glob
• de-duplicates by first selection and retains exact:<name> / glob:<pattern> provenance
• keeps the existing select_model_groups() API as a compatibility wrapper
• routes production build/list/explain through the provenance-aware selector
• carries selection provenance through prepared/generated groups and exposes it in explain
• keeps glob-selected groups behind the existing aggregation eligibility/fail-closed boundary
• preserves fail-fast explain rejection for models outside all configured selectors
• fails closed if model_overrides is configured before the follow-up override implementation exists

Scope boundary

This PR does not apply any compatibility/evidence overrides and does not change exact/foreign mapping rules. The follow-up slice will implement the strict override whitelist against aggregated group evidence.

Tests

Regressions cover exact-only compatibility, glob-only config, duplicate/empty patterns, strict unmatched globs, case sensitivity, lexical deterministic expansion, first-selector de-duplication/provenance, LiteLLM row-order independence, ineligible glob-selected groups failing aggregation, selection provenance surviving generation/explain, configured list ordering, and fail-fast explain behavior.

Refs #5

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