chore: remove obsolete Python shim runtime dependencies

[zackees]

Refs #229. Source audit finds no typeguard or zcmds imports/calls in the remaining six Python shim modules, Rust code, setup.py or CI Python sources. Both remain declared in pyproject.toml and resolved in uv.lock. Meson/Ninja remain required by Rust wasm_build.rs meson setup/compile; uv remains required by _rust_cli.py and native runtime provisioning.

Remove only typeguard and the Windows-conditional zcmds_win32 requirement, update the lockfile, and fix the obsolete ctcb comment. Acceptance: dependency-boundary test RED before the removal, GREEN after; full Python suite and lint; lock consistency. Do not claim removal of active build tools or completion of the kernel migration. No replacement facade is appropriate for unused capabilities.

[zackees]

Implemented on the migration branch: removed typeguard and Windows-only zcmds_win32. Metadata regression observed RED then GREEN; full Python suite 30 passed / 1 skipped, Ruff and local uv lock consistency pass. Installed distribution metadata reports only meson>=1.4, ninja>=1.11 and uv>=0.5. Note: uv.lock is intentionally gitignored, so its regenerated 23-package reduction is local evidence, not a tracked release change; regression does not require the ignored file. Reviewed clean. Remains coordinated with draft #242 and its overall release gates.

[zackees]

Verified on main (4ebcabd): the installed metadata declares only meson>=1.4, ninja>=1.11 and uv>=0.5. typeguard and the Windows-conditional zcmds_win32 are gone from pyproject.toml, no source under src/ or setup.py references either, and the obsolete ctcb comment is gone. Shipped in #242 (merged 2026-09-15). Tracked in the burndown #262.