feat(depends): implement depends and prohibits commands with shared dependency logic

Add the `depends` (why) and `prohibits` (why-not) commands that query
the dependency graph to answer "which packages require X?" and "which
packages prevent version Y of X from being installed?" respectively.

Introduces the shared `dependency` module with package loading from
lock file or installed.json, forward/inverted dependency graph walking,
recursive traversal with cycle detection, and table/tree output formatters.

Adds `conflict` field to LockedPackage for conflict-based prohibition
detection, updating all struct literals across install, remove, require,
and update test helpers.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/crates/mozart/src/lockfile.rs b/crates/mozart/src/lockfile.rs
index 9b5b996..7c945b8 100644
--- a/crates/mozart/src/lockfile.rs
+++ b/crates/mozart/src/lockfile.rs
@@ -78,6 +78,9 @@ pub struct LockedPackage {
     )]
     pub require_dev: BTreeMap<String, String>,
 
+    #[serde(default, skip_serializing_if = "BTreeMap::is_empty")]
+    pub conflict: BTreeMap<String, String>,
+
     #[serde(skip_serializing_if = "Option::is_none")]
     pub suggest: Option<BTreeMap<String, String>>,
 
@@ -281,6 +284,7 @@ fn packagist_version_to_locked_package(name: &str, pv: &PackagistVersion) -> Loc
         dist: pv.dist.as_ref().map(packagist_dist_to_locked),
         require: pv.require.clone(),
         require_dev: pv.require_dev.clone(),
+        conflict: pv.conflict.clone(),
         suggest: pv.suggest.clone(),
         package_type: pv.package_type.clone(),
         autoload: pv.autoload.clone(),
@@ -527,6 +531,7 @@ mod tests {
             }),
             require: BTreeMap::new(),
             require_dev: BTreeMap::new(),
+            conflict: BTreeMap::new(),
             suggest: None,
             package_type: Some("library".to_string()),
             autoload: None,
@@ -954,6 +959,7 @@ mod tests {
                 dist: None,
                 require: BTreeMap::new(),
                 require_dev: BTreeMap::new(),
+                conflict: BTreeMap::new(),
                 suggest: None,
                 package_type: None,
                 autoload: None,
@@ -976,6 +982,7 @@ mod tests {
                 dist: None,
                 require: BTreeMap::new(),
                 require_dev: BTreeMap::new(),
+                conflict: BTreeMap::new(),
                 suggest: None,
                 package_type: None,
                 autoload: None,