* ci: share the gate dependency-cache key and read-only restores
* fix(rust-cache): compare cache directories, not their spelling
A Windows runner spells one directory two ways: git-bash reports $HOME/.cargo as
/c/Users/x/.cargo, and a native tool or workflow input passes C:\Users\x\.cargo. The
align-environment guard compared the strings, so the first Windows caller copying the
README example exited 1 with "sets ...; drop the input". It now resolves both sides when
they exist and otherwise normalises backslashes, a drive letter and its case before
comparing. Refusing a genuinely different cargo home is unchanged.
Regressions cover both Windows spellings, a trailing separator, a drive letter in either
case, two different Windows homes, and a symlinked home that resolves to $HOME/.cargo;
the five positive cases fail against the previous guard.
