chore: rename packages/ to crates/

Move all 29 workspace members from packages/<name>/ to crates/<name>/.
Updates: workspace Cargo.toml (members + path deps), justfile, root
CLAUDE.md, scripts/build/CARGO_INSTALL.md, docs/architecture/crates.md
(renamed from packages.md), structural references in docs/architecture
and docs/configuration, per-crate CLAUDE.md self-references. Historical
plans, reports, and building/ docs are left untouched.

No behavior change; just check-all stays green and fermata tests pass.

src/core/project.rs

@@ -0,0 +1,27 @@
+use std::path::{Path, PathBuf};
+
+/// Markers checked in priority order when walking up from a target path.
+const MARKERS: &[&str] = &["botignore.toml", ".botignore", ".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
+/// any marker in `MARKERS`. Walks from the **target file's location**, not
+/// from cwd, because agents `cd` around.
+pub fn find_project_root(target: &Path) -> Option<PathBuf> {
+    let start = if target.is_file() {
+        target.parent()?
+    } else {
+        target
+    };
+
+    let mut current = Some(start);
+    while let Some(dir) = current {
+        for marker in MARKERS {
+            if dir.join(marker).exists() {
+                return Some(dir.to_path_buf());
+            }
+        }
+        current = dir.parent();
+    }
+    None
+}