feat(apply): cross-repo blast-radius in the plan preview

§7 M3 (part 2): planning a change to a GROUP node now reports the descendant
apps owned by OTHER projects that the change fans out to — the cross-repo
signal an operator needs before touching shared config.

- OwnershipPreview gains `blast_radius: Vec<ProjectImpact>`; `group_blast_radius`
  walks the group's subtree (recursive CTE) and groups descendant apps by their
  nearest-claimed-ancestor project, excluding the planning project. Ancestor
  resolution is memoized per group (one walk per distinct descendant group, not
  per app).
- `pic plan` renders `blast_radius` rows (mode-agnostic).
- the apply_ownership journey gains a plan-preview case pinning both the
  ownership annotation (claim / conflict) and the blast radius (two other
  projects' apps surfaced) end to end.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/picloud-cli/src/cmds/plan.rs

@@ -74,6 +74,15 @@ fn render_tree(plan: &TreePlanDto, mode: OutputMode) {
                 o.owner.clone().unwrap_or_default(),
                 String::new(),
             ]);
+            for b in &o.blast_radius {
+                table.row([
+                    node.clone(),
+                    "blast_radius".to_string(),
+                    b.project.clone(),
+                    format!("{} app(s)", b.apps),
+                    String::new(),
+                ]);
+            }
         }
         let groups: [(&str, &Vec<ChangeDto>); 8] = [
             ("script", &n.scripts),
@@ -203,6 +212,14 @@ fn render(plan: &PlanDto, mode: OutputMode) {
             o.owner.clone().unwrap_or_default(),
             String::new(),
         ]);
+        for b in &o.blast_radius {
+            table.row([
+                "blast_radius".to_string(),
+                b.project.clone(),
+                format!("{} app(s)", b.apps),
+                String::new(),
+            ]);
+        }
     }
     let groups: [(&str, &Vec<ChangeDto>); 8] = [
         ("script", &plan.scripts),