API to control what is ignored and `--no-ignore` ability to index everything

[fdncred]

For nushell I'd like to be able to have a --no-ignore flag or --ignore [*.rs *.md *.js] parameter to control what is ignored during indexing.

I'm having a hard time telling exactly what is ignored now and I'm getting a lot of, "we have yyy number files in this tree but idx is only seeing zzz number of files". I'm not sure if something is wonky on my implementation, files are being ignored, an upstream bug here, or working as expected. Having a --no-ignore option would help narrow that down because then it should be reporting every file in a tree regarless of ignore state.

If there already is something, I apologize, I didn't see it here https://docs.rs/fff-search/latest/fff_search/ but I could be missing it.

[gustav-fff]

[triage-bot] FEATURE REQUEST:

Currently ignore behavior is hardcoded in `crates/fff-core/src/file_picker.rs:1738-1751`:

```rust
walk_builder
.hidden(!is_git_repo)
.git_ignore(true)
.git_exclude(true)
.git_global(true)
.ignore(true)
...
if !is_git_repo && let Some(overrides) = non_git_repo_overrides(base_path) {
walk_builder.overrides(overrides);
}
```

Plus extra non-git ignore list in `crates/fff-core/src/ignore.rs:3-39` (`node_modules`, `target/debug`, macOS `Library/*`, etc.) and binary-extension skip at `file_picker.rs:1781` for non-git roots. No public API to override any of this — `fff-search` (= `fff-core`) takes none of these as scan params.

So discrepancy you see vs raw tree count is expected: `.gitignore` + `.git/info/exclude` + global gitignore + hardcoded dirs all apply.

Needs maintainer scoping (@dmtrKovalenko): which knobs to expose (bool no-ignore vs full ignore-list override), and on what API surface (Rust `fff-search`, MCP, Lua). Holding off on a PR until direction is decided.

Honk-Honk 🪿