Adds the FixIt collector + per-file unified-diff patch writer
behind a new `fold scan --fix-output <path>` flag. Patch-only --
no in-place rewrites -- so a bad suggestion can't silently
overwrite source.
Consumers (only when the transform is provably sound):
- UninitLocalRead: scalar integer locals only.
`int x;` -> `int x = 0;`. Non-scalar types deferred.
- DeprecatedApi: regex extracts `[Uu]se foo()` from the
deprecation message; silent skip when unparseable rather
than hallucinating a rewrite.
Patches include 3 lines of context above + below each fix so
`git apply --check` accepts them. End-to-end verified against a
synthetic fixture.
