3a03f07560 qt: Avoid header circular dependency (Anthony Towns)
25884bd896 qt, refactor: Move `FreespaceChecker` class into its own module (Hennadii Stepanov)
Pull request description:
For some reason, the MOC compiler in older versions of Qt 6 fails to parse `qt/intro.cpp`, as noted in [this comment](https://github.com/bitcoin/bitcoin/pull/32998#issuecomment-3082011233).
This PR proposes a move-only refactoring to simplify the source structure by eliminating the need for the inline `#include <qt/intro.moc>`, thereby effectively working around the issue.
Required for https://github.com/bitcoin/bitcoin/pull/32998.
ACKs for top commit:
ajtowns:
ACK 3a03f07560
Tree-SHA512: 4a7261f04fff9bd8edd4dc2df619c90e06417e19da672dd688a917cd0b9a324a6db7185a47c48f0385713b5e6c45d2204bef58cbe6c77299386136ed5682bd8d
e6bfd95d50