FlowDrop 2.0.0-alpha14

A single-fix release, out one day after alpha13 because that release is
what broke this.

Fixed: a `mixed`/`any` input port refused every structured value at the
launch and session-turn doors. `SchemaFragmentChecker::kind()` had no arm
for `mixed`/`any`, so a port declaring no constraint at all checked as
`string` (`is_scalar()`) and refused arrays and NULL with "expected mixed,
got array" — while `ParameterResolver` accepted the same value once the
run was under way. `mixed` is the port editor's default `dataType`, so
this sat on the default authoring path.

No schema updates, no post_update hooks, no configuration changes.