Kudzu 0.8.28 - Source-local binding index

Adds the first large-application compiler foundation: deterministic source-local lexical identities for locals, parameters, imports, captures, globals, and unresolved references. Reactive binding discovery and lowering now preserve shadowing correctly, synthesized keyed expressions retain their fail-safe path, and no browser runtime bytes or public API were added. Validation: npm run check, all 185 tests, and packed-package smoke.