feat: build system hardening — collision detection, validation gates, init path enforcement

5-phase hardening to prevent silent file-layer collisions (the D-Bus
regression class):

Phase 1: lint-config-paths.sh + make lint-config in depends.mk
Phase 2: CollisionTracker in installer (content-hash comparison)
Phase 3: installs manifests in recipe.toml + validate-file-ownership.sh
Phase 4: validate-init-services.sh + make validate in disk.mk
Phase 5: documentation (AGENTS.md, BUILD-SYSTEM-HARDENING-PLAN.md)

Both redbear-mini and redbear-full build and validate clean.
66 declared install paths in base, zero conflicts.

src/recipe.rs

@@ -130,6 +130,8 @@ pub struct PackageRecipe {
     pub dependencies: Vec<PackageName>,
     pub version: Option<String>,
     pub description: Option<String>,
+    #[serde(rename = "installs")]
+    pub installs: Vec<String>,
 }
 
 #[derive(Debug, Clone, Default, Deserialize, PartialEq, Serialize)]