fix(ci): make verdict-backtest checks deterministic

[mrnicholasbcarter-code]

Summary

• Replace undefined-extra/fallback CI installation with the declared dev/viz dependency contract.
• Run deterministic Python 3.10/3.11/3.12 test matrix, lint, format, and mypy checks.
• Add package metadata/Twine validation and isolated wheel/sdist import smoke tests.
• Align repository docs and example paths with verdict-backtest while preserving backtest_harness imports.

Fixes #9

Evidence

• Code Review Graph diff analysis: low risk (0.40); existing graph flags 9 untested analytics symbols outside this CI-only scope.
• 18 tests passed (one pre-existing pytest config warning for asyncio_mode).
• Ruff check and format check passed.
• MyPy passed.
• Build and Twine checks passed.
• Isolated wheel and sdist installs imported backtest_harness.
• git diff --check passed.

[mrnicholasbcarter-code]

Independent exact-diff review completed: CI installs declared extras deterministically, package artifacts are checked in isolated environments, and all required checks are green; self-approval is unavailable for the PR author.