docs(website): correct inaccurate feature descriptions

A full audit against actual app behavior found several stale/wrong
claims: a nonexistent Settings lock toggle and right-click menu in
floating mode, overstated per-core sparklines on the CPU panel,
hardcoded battery power thresholds that don't match the configurable
defaults, a missing Website link in the About dialog description, and
the sensor install described as a scheduled task instead of the
Windows Service it actually is.

Closes #162