Two improvements while investigating #147:
1. `obscura --version` / `-V` now print the CARGO_PKG_VERSION instead of
erroring out. The issue reporter explicitly called out that there was
no version flag, and the existing `obscura serve` banner is the only
way to discover the version.
2. New regression test in obscura-js verifies that a TypeError thrown
from one script does not poison the runtime: subsequent scripts and
DOM queries must continue to work. The reporter's symptom was that
offside.js crashing collapsed --dump text output to 1 byte; that
cascade should never happen and this test pins it down.
The classList error itself is offside.js's own bug (it indexes into the
querySelectorAll result without checking for an empty array) and only
fires when the .slideout-navigation element is absent from the DOM.
On current main that element parses correctly and offside.js runs
without error against a captured copy of the affected page.