feat(apply): declarative extension_points reconcile (§5.5 C3)

Thread extension-point markers through the manifest and the apply engine —
a name-only resource modeled on `secrets` (shape) with `vars`-style
create/prune write behavior.

- manifest: top-level `extension_points = ["theme", …]` (allowed on app and
  group; overlay stays base-only via deny_unknown_fields); `build_bundle`
  emits the names.
- apply_service: `Bundle.extension_points`, `CurrentState.extension_point_names`,
  `Plan.extension_points` (+ is_noop), `diff_extension_points`
  (declared→Create / live-undeclared→Delete / else NoOp), `load_current`
  loads them, `reconcile_node_tx` inserts on Create + deletes on prune,
  `state_token_with_names` folds in `ep|<name>`, `validate_bundle` rejects
  duplicates + reserved names, `ApplyReport` gains created/deleted counts.
- CLI client + plan/apply rendering: `extension_points` in PlanDto/NodePlanDto/
  ApplyReportDto, an `extension_point` row group in `pic plan`, a count in the
  apply summary.

pull sets it empty for now (wired to the read endpoint in C4).

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

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

@@ -64,12 +64,13 @@ fn render_tree(plan: &TreePlanDto, mode: OutputMode) {
     let mut table = Table::new(["node", "kind", "op", "resource", "detail"]);
     for n in &plan.nodes {
         let node = format!("{}:{}", n.kind, n.slug);
-        let groups: [(&str, &Vec<ChangeDto>); 5] = [
+        let groups: [(&str, &Vec<ChangeDto>); 6] = [
             ("script", &n.scripts),
             ("route", &n.routes),
             ("trigger", &n.triggers),
             ("secret", &n.secrets),
             ("var", &n.vars),
+            ("extension_point", &n.extension_points),
         ];
         for (rk, changes) in groups {
             for c in changes {
@@ -160,6 +161,7 @@ pub fn build_bundle(manifest: &Manifest, base_dir: &Path) -> Result<Value> {
         "triggers": triggers,
         "secrets": manifest.secrets.names,
         "vars": vars,
+        "extension_points": manifest.extension_points,
     }))
 }
 
@@ -174,12 +176,13 @@ fn tagged(kind: &str, spec: impl Serialize) -> Result<Value> {
 
 fn render(plan: &PlanDto, mode: OutputMode) {
     let mut table = Table::new(["kind", "op", "resource", "detail"]);
-    let groups: [(&str, &Vec<ChangeDto>); 5] = [
+    let groups: [(&str, &Vec<ChangeDto>); 6] = [
         ("script", &plan.scripts),
         ("route", &plan.routes),
         ("trigger", &plan.triggers),
         ("secret", &plan.secrets),
         ("var", &plan.vars),
+        ("extension_point", &plan.extension_points),
     ];
     for (kind, changes) in groups {
         for c in changes {