v0.3.6

Patch release. Wires up the missing `--global` flag on
`mainwp skill install`.

Before this fix, `mainwp skill install --global` failed with
`Unknown option: --global (run: mainwp skill install --help)`
because the case statement in `cmd_skill_install` only knew
about `--all` and `--agent NAME`. The user reasonably
expected `--global` as a shortcut for the most common install
target (`~/.agents/skills/`, the agent name literally called
`global` in the help text and the picker).

After this change, `--global` appends `global` to the agents
array, which is the same code path `--agent global` would
take. The help text is updated to document the new flag.

`mainwp skill install --global` is now equivalent to
`mainwp skill install --agent global`. `--all` and
`--agent NAME` are unchanged.

61 smoke tests, all passing. Upgrade with
`brew update && brew upgrade mainwp`.