fix(fermata): .botignore no longer stops project-root walk-up

Only .git, botignore.toml, and .botignore.toml define project boundaries.
A bare .botignore is a policy file, not a root marker.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/core/project.rs

@@ -1,7 +1,7 @@
 use std::path::{Path, PathBuf};
 
 /// Markers checked in priority order when walking up from a target path.
-const MARKERS: &[&str] = &["botignore.toml", ".botignore", ".git"];
+const MARKERS: &[&str] = &["botignore.toml", ".botignore.toml", ".git"];
 
 /// Walk upward from `target` (or its parent if `target` is a file) looking
 /// for the nearest project root. Roots are identified by the presence of