Bug: constraint-only git-status queries return 0 results in file search

[0xferrous]

Summary

Queries like git:modified / status:modified are parsed as pure constraints with an empty fuzzy query, but file search incorrectly treats the raw query text as fuzzy text and returns zero matches.

Reproduction

Repository state:

git status --short
# example
#  M flake.nix
#  M crates/fff-nvim/Cargo.toml

Run a file search with a constraint-only query:

git:modified
# or
status:modified

Actual

The search returns zero matches even though the repository has modified files.

Expected

Modified / untracked files should be returned and sorted by frecency / modified-time scoring, even when the query contains no fuzzy text.

Example expected behavior:

flake.nix
crates/fff-nvim/Cargo.toml
...

Acceptance criteria

• git:modified returns modified/untracked files
• status:modified returns modified/untracked files
• constraint-only queries do not reuse raw_query as fuzzy text
• a regression test exists for this behavior

Regression test

See:

• crates/fff-core/tests/known_bug_constraint_only_git_status_query.rs

That test was added as a repro for this issue. On buggy revisions it fails with total_matched=0.