python: add initial package, CLI, and runtime bindings

[tpn]

Summary

• add an initial Python package scaffold with uv, hatchling, ruff, black, mypy, and worktree-local pre-commit hooks
• add a Typer-based CLI foundation with offline ph create and ph bulk-create paths aligned to the existing C CLI workflows
• add an initial programmatic Python runtime path via rawdog_jit plus a backend-neutral Table / build_table() API
• refactor native binary/library discovery to prefer install-style prefixes over development-tree fallbacks
• add user-facing docs and project ledgers for the Python CLI/API work

Notes

• this is an initial Python foundation PR, not a claim that the Python package is complete
• offline CLI and in-process runtime are intentionally kept separate
• end-user packaging is being steered toward wheel-bundled _native artifacts and conda-prefix discovery, with an editable-install helper for source checkouts

Validation

• env -u PYTHONPATH uv run pytest
• env -u PYTHONPATH uv run ruff check python_src python_tests
• env -u PYTHONPATH uv run black --check python_src python_tests
• env -u PYTHONPATH uv run mypy

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[tpn]

Addressed the remaining review feedback in commit 588bf8f by replacing the depth-based source-tree fallback root logic with a structural source_checkout_root() helper and by updating the regression tests so they no longer depend on the temporary worktree name.