[Feature] tox for Python test/lint matrix + Rust MSRV verification #30

What problem does this solve?

tools/*.py claims "Python 3.8+ compatible" (README badge, docs/CONTRIBUTING.md) but nothing actually verifies that across versions — there's no Python job in CI at all, and the only local check is a handful of ad-hoc --help/smoke commands in Makefile's test-python target. This project has already shipped Python-version-shaped bugs before (see PR #29's fix for a syntax error that broke claude-pipeline on every version) that a real test suite would have caught immediately.

Similarly, rust/claude-tools declares a "Rust 1.75+" badge in the README but nothing enforces that MSRV — CI only builds against stable, so a dependency bump or a new-syntax usage could silently raise the real minimum version without anyone noticing.

Proposed solution

• Python: add tox.ini + a small tests/ pytest suite covering all 8 CLI tools (functional, sandboxed HOME, subprocess-based — the same technique used to manually verify PR Add autonomy levels (L0-L4), claude-lessons tool, and MCP server guide #29). tox environments: py38..py313 (skip missing interpreters), lint (ruff check), fmt-check (ruff format --check). Wire into Makefile (new make tox target) and a new CI job running the matrix via actions/setup-python.
• Rust: declare rust-version = "1.75" in rust/claude-tools/Cargo.toml (matches the README badge, makes cargo itself enforce it for consumers), add an MSRV job to CI (cargo msrv verify via cargo-msrv, the closest Rust-ecosystem equivalent to tox's multi-version testing), and a make msrv target.

Alternatives considered

Rewriting tools/*.py as an installable package (pyproject.toml + pip install -e .) so tox could use its normal package-based flow — rejected as unnecessary scope increase; these are standalone CLI scripts, not a library, and docs/CONTRIBUTING.md deliberately keeps them dependency-free and copy-paste-installable. tox.ini with skipsdist = true running pytest directly against tests/ gets the version-matrix benefit without that.

Additional context

Depends on tools/docs from #26/#27/#28 (PR #29) — this branch builds on top of it.